How do you communicate rules to little kids?

I want my lessons to be enjoyable as well as safe, but I recently got a very rambunctious group of 3 year olds who have a lot of confidence and comfort in the water. Only problem is their confidence and comfort is unfounded. They will try to pop into the water without knowing how to come up for air the second I am engaging with a different student.

I was hoping for tips on how to communicate rules for lessons for little ones because I have a feeling that how I communicate them is the problem.

How do you talk to your younger swimmers about the rules?