There are some drawbacks, IMHO, to Sci-Fi when you've got young kids.
The restaurant is incredibly dark. So dark that it is hard to read a menu or see your food clearly. This can be extra challenging when you've got little ones.
Also, the cars (which are the draw) only seat 2 people per-seat, and of course the seats are all facing forward. This means that you will sit with one child in one row and your spouse will sit in another row with the other child (unless you request to sit at the tables in the back, and forego the cars). Even with having an 11-year-old, this is weird/uncomfortable for me (DH and DS sit together in one row and I sit by myself behind them -- yuck!).
And depending on how sensitive your older child is, the movie clips they show could be an issue. We first took DS when he was 6 and he was utterly traumatized by the experience because he was SO sensitive to the images (to him they weren't silly, they were scary). Took us years to get him to try it again, and during that time he'd complain about how horrible that first experience was!
So, yeah, if it were me I'd go for 50s Prime Time! (Plus we think their food is better!)