Why not take an excursion to the Belize zoo? It is supposed to be nice. They have a website at http://www.belizezoo.org
Or, arrange a private excursion that suits the needs of your family. We are using Sea Sports Belize for our family excursion, they will plan an excursion just for you.
Don't miss Belize. I know some people may be turned off by the poverty of the city, but get out of the city and see the beautiful country or visit the cayes. We chose our cruise specifically to see Belize.