just got back last week from AC, stayed at Xanadu. great place, we put our kids on the handle bars of the bikes and rode all over, like the locals do.
my son did get some pica pica the first day we snorkeled, but put some benadryl lotion on it, supplied by the guide, and he was fine. saw no bugs the whole time, and we were 3 days inland too.
have a great time,
you might want to check the cruise ship calendar (google it) for which cruise ships will be in port in Belize while you're there, they do do some day trips to the ruins, cave tubing, etc.