2 mistakes in the movie

Your first comment isn't a goof. While it appears to be a cardboard prop, the plate on Kelly's car is done correctly. In 1956, California issued new license plates with a yellow base plate and black letters. In the top right corner, the plates have a black strip with a yellow "56" to indicate the year they were issued. This black strip with "56" remained on the plates after 1956, so plates issued in 1957 and after also had them.

Originally, the the State was going to issue a small metal tab that fit in to slots and went over the "56" to indicate the owner renewed the plates. The state decided to issue stickers instead of metal tabs. The stickers were placed on the top of the plate between "CALIFORNIA" and "56". Since the State went with stickers instead of metal tabs, the slots for metal tabs were not on later plates.

Here is what a California license plate with a 1961 renewal sticker looks like (note the tab slots on each side of the black strip):
http://img23.imageshack.us/i/california1961aek438.jpg/
Here is an image of Kelly's car as it pulls in to the garage (I have put a square around the renewal sticker):
http://img693.imageshack.us/i/eit002.jpg/

With regard to Toby (Kelly's sister), I wondered about that too. However, it's not necessarily an error. Toby may have been able to open the door, but when Red was there, she realized she was probably safer in that closet. So she may have simply chosen to stay there after he left. Also, when the officials find her, she is standing against the wall with a look of extreme distress/shock. She may have just been paralyzed with fear, and she was afraid to come out.

I must also add that that was a very brave scene for her to do in 1962.

I figured there was a handle on both sides of the door, but that the handle on the outside could be locked in position? Seems like the most probable solution...