Peter learned to use his mask and snorkel in the tub before we tried the ocean and it really helped. Remember, snorkeling is a training. Practice makes perfect, and beginning practice is preferably in calm, shallow water, perhaps no deeper than your child's arm is long. While floating face down while wearing a mask and snorkel, even the view of fingers playing in the sand at arm's length is rewarding. And there are fish surprisingly close to shore.
Shallow areas are ideal for experimenting with bouyancy.
Salt water supports snorkelers better than the fresh water of pools, and developing a confident ability to float is a major step towards safe, relaxed snorkeling. Children have such varied reactions to the sea. Some are filled with trepedation, others jump in with boundless enthusiasm. Mark and Jessie took the methodical approach. We took the entire first day to become comfortable with the water and the equipment.