Children who are at least 3 years old can join manatee snorkeling tours. However, it's critical that all participants be calm and quiet so that they don't startle the manatees. As a mom of two kids I would say that calm, water-confident kids can have a great time as young as 7 or 8. Because of the water temperature, our kids couldn't stay in the water as long as we did but at 9 and 12 they were able to hang out on the boat without needing a parent.