Community Hall should have some activities that will be fun. There is a play area nearby, and a very shallow kids pool area the 4 year old could play in with the babysitter there with the baby. I think it was 12-18" deep. DTD would be my other choice, unless the babysitter is very confident about doing a park and getting home okay with the kids and probably a stroller. At least at DTD it is small enough in the Marketplace area they can play on the play sets, play with some legos and then take a boat back.
For dinner you can have them get it at Goods to Go - either fast food or order from Olivia's menu and take it back to the room. Or order pizza to the room.