You can also try this company http//www.coralbreezelimited.com I went on their shark ray alley snorkle tour in April, and I highly reccomend this company very professional staff who were very fun. They offer other trips such as a day at the beach, and snorkling or observation of snorkling. There is also a Baboon sanctuary in Belize, the baboon here are really monkey I belive and you can feed them. I've heard that was enjoyable.
my family and i, two adults and 3 kids, 8,10,12
went cavetubing with http://www.cbelize.com Marcel our guide was quite helpful, and did share lots of information about his country. on their site they have a variety of tours displayed.