How old are the kids? Discovery Cove has limits on who can do the Dolphin Swim. The "resort pool" area is warm water and mostly shallow. The lazy river is deep and runs very fast. The snorkeling area has a small shallow area then mostly deep. The water by the animals is not deep and easy to manage. Absolutely put on their wet suits AND the life jackets. They are available all over. They are also good for adults who enjoy snorkeling long periods of time, it is much less exhausting.
I have been many times and have seen very few kids under the age of about 8. It is a lot of money to spend to just play in the resort pool area.