Where is Richard Carlson in this Movie and Who is Thomas Stevens Jr.?

I'm confused by the IMDb credits for The Day the Earth Stood Still. They refer to a character called "Thomas Stevens. Jr.", who presumably would be the son of the character "Tom Stevens" who is dating Patricia Neal's character. But in the movie, Tom Stevens does not have a child (as far as I know); it is Patricia Neal's character who has the son. And even if he did have a son, the son would presumably be young, i.e. somewhere between about 5 and 15 years old. But the actor who supposedly plays "Thomas Stevens Jr." is Richard Carlson, who was born in 1912 and therefore would be 39 when the movie came out. Carlson couldn't credibly play the young son of Tom Stevens when he was himself nearly 40 (and only a year younger than actor Hugh Marlowe who plays Stevens). So something is screwy about the credits here.

Is it possible that some IMDb fan has confused Carlson with Marlowe, and put in a false credit here? I know that for years I confused Marlowe with Carlson, as they look superficially alike, and have similar voices and act in a similar manner.

Or is there some other "Thomas Stevens Jr." character in the movie who is not supposed to be related at all to Tom Stevens, the boyfriend? Then the name similarity would be purely accidental.

Any help would be appreciated.