Can your kids put their faces in the water and keep eyes open with or without a mask? Then they will probably do O.K. My kid's swim coach says there is a certain type of kid swimmer, those who love masks and snorkels and will keep their faces in the water, then there are others who hate it, even if they swim well. Try to find snorkel gear that fits the kids well, teach them the proper way to clear the mask and snorkel in a pool or dead calm water. If they know how to do these things without thinking then they will do fine in the waves and bobs of the ocean. The unfamiliarity of the gear and the ocean waves can be freaky even to an adult.
Carla