Skip Mars 2112- it stinks imho.
And holy moley skip the chains while you are in NYC- overpriced and not as good as you find at home. Plus there is a whole world of cheap eats out there.
For your son and anyone that's into tech this is FREE
http://wondertechlab.sony.com/index.html
My son enjoyed it - it's about an hour worth to do.
Favorite dinner spot
Becco
They do a pasta special everyday of 3 different pastas- it's all you can eat. And it's generally delicious. It's about $18 for lunch and $22 for dinner I think. It includes either a cesear salad or an Anitpati Misto(including seafood!!!) It's a great deal and the food is fantastic!
http://becco-nyc.com/
Oh and it's child friendly.
Don't avoid all the carts. Some of them are fantastic. I've eaten at them my whole life and I"m still alive.
Ethnic places are generally cheaper.
I like Ellen's Stardust for breakfast- singing waitstaff and it's not expensive imho. So you get breakfast and a show.
You'll have a blast. And yes get there early and make sure you find a spot near a bathroom!! It can be freezing too so bring blankets! And have a great time. It's my favorite time in the city.