Houston with kids!

We are going on a 2 week vacation in Houston over Easter. We are going to visit my brother-in-law. He has no children, so he is not very good at ideas for activities. We have children aged 3, 8 and 15. Our 8 year old is very visually impaired. Does anyone have any good suggestions for activities, restaurants, museums or anything else? Is there a restaurant with singing waiters or something like that? Last time we went to aquarium and childrens museum. Thanks.

Edit: We're coming from Denmark (a little country i Europe)