M.O.
My husband and I did our honeymoon there. We stayed by the beach at Placencia and snorkeled there -- it was unbelievably beautiful and tranquil. We also took a guided tour of the rainforest and explored the Mayan ruins of Tikal. And, probably the most memorable part of the trip was when we did a homestay with a Mayan family with 14 kids. When they found out that my husband and I grew up in families with 2 and 3 kids respectively, they were SHOCKED. This is a wonderful, educational, eye-opening way to travel, and it's incredibly safe and kid-friendly. I'd love to go back now that my son is at a good traveling age.
In terms of safety, the city of Belize can be dangerous, as can the Guatemalan border, but the beach and the rural/wilderness interior are incredibly safe. It's a beautiful country with a real culture of graciousness and hospitality. I recommend it to the skies.