What would the criminal charge(s) and punishment have been for them?

This is a difficult question. First of all, you cannot really determine whether they could be charged with conspiracy to commit a crime because it is unclear whether their plan would have constituted a crime to begin with. From what we know, their plan was to dare George to strip naked and jump in the river. Then, they were going to abandon him. Whether they could be charged with conspiracy for this depends on whether Oregon has a criminal statute outlawing this underlying behavior of daring George to strip naked, jump in the river, and then abandoning him. Maybe some sort of criminal mischief law? Theoretically, there could be.

Anyhow, assuming there was a crime on the books for this type of behavior, conspiracy requires an agreement between two or more persons and an overt act in furtherance of the agreement. Rocky, Marty, Clyde, and Sam made the agreement. Millie never did. The overt act requirement was satisfied when they went to pick up George to bring him to the river. If there truly was some sort of mischief law that made their plan illegal, Rocky, Marty, Clyde, and Sam would be charged with conspiracy for this crime. Most likely, Millie would not. She did not know what the plan was until Sam told her in the forest, and she immediately told Sam that he either told Rocky to call it off or she would leave. She never had the appropriate mens rea for conspiracy. Now, if when Sam told her in the forest the plan and agreed to it and carried on with her day, then she would be liable for conspiracy. But she did not. Therefore, she would be exonerated on this charge. Rocky, Marty, Clyde, and Sam would not have any defenses here, Marty especially since he never even wanted to abandon the conspiracy. Rocky, Clyde, and Sam, on the other hand, would argue that they tried to abandon the conspiracy. However, the test for abandonment of a conspiracy is whether they thwarted the plan by either convincing the other co-conspirators to not follow through with the plan, or by calling the police. They never did either successfully. Therefore, they would all be charged, assuming that there is a law on the books for their behavior.

The next inquiry is whether the Pinkerton Rule for conspiracy is in effect in this jurisdiction. The Pinkerton rule makes conspirators liable for any reasonably foreseeable consequences of their conspiracy. The question falls on whether it was reasonably foreseeable that Rocky would push George into the river, causing George to drown. If so, Rocky, Marty, Clyde, and Sam would be charged with the underlying crime that was committed. However, it does not appear that the crime that was committed against George was reasonably foreseeable. Essentially, daring a person to jump in the river naked and then abandoning him does not seem to rise to the level of being the type where it is reasonably foreseeable that he would be pushed into the river. Therefore, they should not be liable under the Pinkerton Rule. Although, it was interesting that Marty somehow believed that they planned to injure George, which Clyde immediately responds to this and says that it was an accident and accidents happen to kids all the time. This part is pretty reflective on the guilty conscience that Marty did have.

Now, whether they will all be charged as accomplices for George's death is another story. Here, Rocky was the principal actor (the one who actually pushed George into the river), where Marty, Clyde, Sam, and Millie may be considered the accessories. The test for accomplice liability is whether the parties involved aided or abbetted the crime committed against George. In this case, it looks like the crime was involuntary manslaughter. Clyde, Sam, and Millie were probably not accomplices here. They did not do anything other than sit there in the boat. However, Marty could arguably be considered an accomplice in this situation. The prosecution could make a case and say that Marty aided and abbetted the crime when he began to walk toward George and attempted to attack him on the boat, and had the requisite reckless mens rea for involuntary manslaughter considering that they were on a boat, and he was uncertain whether George could swim. The fact that George could not swim would certainly not be a defense though if either Rocky or Marty tried to argue that his conduct was not reckless because they were uncertain about this fact. Personally, I would say there is a good chance for Marty to also be charged with involuntary manslaughter as Rocky's accomplice as an aider and abbetor based on his actions of attempting to attack George on the boat.

Involuntary manslaughter for Rocky is pretty locked. He negligently pushed George into the water, and his mindset was reckless. However, he would probably not be charged with anything more than involuntary manslaughter. He may try to argue that his actions were involuntary in the sense that he should not even be charged with involuntary manslaughter, however. Essentially, he may try to say that his action of pushing George was a reflex movement and something that he did not have control over. This is hardly plausible though. Certainly, there was a lot of commotion, but his actions were not physically coerced, nor were they reflexive. He will be charged with involuntary manslaughter.

Now, for concealment of the body, if I'm recalling correctly, the people who dug out the grave were Rocky, Marty, Clyde, and Sam. They were all the principal actors. Millie would be the accomplice here. The question is whether she aided and abetted conealing the body. No, she did not. She was there, but she did not aid and abet this. Rocky, Marty, Clyde, and Sam all dug the grave and had the mens rea to conceal the body. They should be charged with this, provided that there is not an abandonment defense. Rocky, Clyde, and Sam may be able to argue that they abandoned their plan to conceal the body once they called the police and told them where the body was. This is a plausible argument. Marty, on the other hand, would probably not have this as a defense and should be charged with it. Millie would be completely exonerated for this.

Finally, Marty would be charged with armed robbery and unlawful flight to avoid prosecution.

Overall, when all is said and done, this is how it would probably break down:

Rocky: Conspiracy (if the underlying plan was a crime), involuntary manslaughter, concealment of a corpse (arguable; may have an abandonment defense).

Marty: Conspiracy (if the underlying plan was a crime), involuntary manslaughter (possibly as Rocky's accomplice), concealment of a corpse (no abandonment defense for him), armed robbery, and unlawful flight to avoid prosecution.

Clyde: Conspiracy (if the underlying plan was a crime), concealment of a corpse (arguable; may have an abandonment defense).

Sam: Same as Clyde.

Millie: Nothing at all.

As for their punishments, Millie would most likely not be punished for anything. Perhaps the judge would make her do some sort of community service simply for associating with the others, but she would suffer nothing substantial. Also, even assuming that they were all charged as adults, I'm not so sure that any of them would do any time with the exception of Marty. Whatever they conspired to do, it was probably not the type that would have a harsh prison sentence. Involuntary manslaughter for Rocky, if he were a first-time offender, he may not do time at all. Granted, he did attempt to hide the corpse, but almost immediately afterward, they called the police. I think a judge and/or jury would have a lot of sympathy for Rocky. Sam and Clyde would almost definitely not do any time. Obviously, Marty would be in the most trouble. He would probably do 5-8 years, maybe even more.

Also, you mentioned second-degree murder for Marty. You sounded skeptical about this charge though, and you had good reason to be. I highly doubt they would be able to get him with second-degree murder for this. By definition, second-degree murder is when a person acts with reckless indifference. The usual test is whether the person cared that they may be taking the life of another. I don't think it's fair to say that Marty, although in a heat of passion, did not care whether George died at that time. The look on his face once he realizes that George cannot swim is pretty telling that Marty did not have a reckless indifference as to whether George lived or died, regardless as to what George said.

well hiding a body is a felony even so i think if they didnt testify against him they would get 2nd degree murder fo sho...but since they are in oregon and not an exactly strict state...i agree with man slaughter but itd be a very easy 2nd degree murder case

What makes you think all the other kids were planning to pin the blame on Marty?

Assuming they tell the truth, I doubt there will be any serious charges. Maybe operating a boat without having a pfd for each passenger?

Rocky would most likely not be charged with manslaughter. There would not be enough evidence to support that charge. While Rocky did knock George into the water, it isn't clear if it was intentional or accidental. He was trying to keep separate two people about to fight in a small boat. The boat was rocking, he may not have had a good footing, Marty was pushing against him, and he may have been off balance. It happened very quickly and there were no good eye-witnesses; no one else was in a position to see Rocky actually hit George.

There would probably be no charge for concealing the body either, given that they went to the police very soon after. Given the kids' ages and relative immaturity, it is understandable that they initially panicked. There would be no "public interest" in pursuing charges.

And that stuff about conspiracy? It is not illegal to conspire to commit a practical joke.

The short answer is they'd do no jail time. Counseling and probation for burying the body, it was the only crime. Marty would've gotten the same if he hadn't robbed the store, he'd probably do time for that.

Well some of the other useless details like the original plan of them tying George up to a tree covered with honey for bugs to bite them and possibly even a bear, and leave him over night. 1st degree. Of course planning a practical joke isn’t a crime but if it were to gone wrong to where it actually kills someone unintentionally or not, that could be 1st degree pre-meditated- Marty even mentions that to Clyde that “We’ve schemed this, from the beginning”. Minute or two before, he was searching around trying to find George’s video camera, which have all the evidence on it. Attempting to obstruct justice or tampering w/evidence… probably obstruction of justice. Marty flashed his wanker to minors- it wasn’t shown on camera but I’m pretty sure the detectives were gonna use their imagination to put two and two together. Millie may not have been part of the plan but she soon knew what they were planning after Sam told her before they put that boat in that water. Rocky pushing George off the boat WAS accidental since he was trying to break up the fight, George the instigator- he have behavioral “problems” but Marty, attempting to hurt George and even making a blank threat, terroristic threat to kill him, I think Marty would do 25 to life. His Brother Kyle, lended him his gun and car, aiding a fugitive (tho he might not know where his brother was going, we could think Marty told Kyle the plan off screen), but we just gonna imagine Marty didn’t tell Kyle what he was planning to do. Since this movie was released in 2004, let’s treat this as if some of this as if their punishments are still going on up to this date, I can agree on what y’all saying, conspiracy not so much but the other stuff, ok. Marty’s the oldest out of everyone so he would obviously be responsible for EVERYONE’S safety, including George’s. & the fact that he was partially the cause of his death allegedly, this would fine him legally responsible. But y’all gotta look at the details, not just the big things.