The Mantas were magical and our tour operator, Jason, gave us so much information about the mantas, he also knew all their names. The one I remember most was Yana, with the broken front fin. We saw 10 different Mantas and they swam up so close to us, and brushed past several of our group members and my kids too (ages 8 and 13).
Definitely breathe easy, stay calm, don't yell, listen to your tour operator, and enjoy the mantas dancing. These were the only tour boat that provided anklet floats for every person, this helps you stay floating and straight with ease. They also provide you with wet-suit tops (only) / full wet suit for kids, and few snacks at the end if you need it. The boat ride is only 5 minutes so don't worry about being cold later. Ofcourse if you intend on watching the sun set as part of the ride then go with tours that are further up north. We preferred eating our dinner and doing the driving a little south to Outrigger resort and so decided to go with the 8pm slot. That way we reduced the boat ride and any possibility of sea sickness which my son is prone to.