The food and service are definately worth 2 credits, but depending on the likes and dislikes for your 12 yo that may sway your choice.
Brown Derby is a replica of the famous Brown Derby in LA. So the inside is pretty upscale. It's done in darker woods and darker carpet. The food is very good. It will be 2 credits vs. the one. There are autographed drawings of the rich and famous all over. ( you will see 2 different color frames - one is for originals that were brought from the LA Brown Derby and one is for the new ones or recreated ones )
50's Prime Time is a different kind of dining experience than the one above. It can be a bit louder, but that's from the laughter. The food here is good also. The gig here is that your waiteress is going to act like your best friends mom.