I don't know much about sports activities, especially how to call them. There are several places, where is possible to rent some kinds of boats and jet-ski. Price for jet-ski is crazy, i dont remember exactly, but i thought it was too much.
Then you can try parachute, which is tied to a boat, a round way was 250 KN, banana tied to a boat for 5 people is a bit cheaper and there are more stuff like this.
I think children must enjoy these activities a lot.
Equipment: Nothing to bring.
Adriatic sea is amazingly clean and blue, it is the best for snorkeling. The only problem is that there are not many animals to sea close to the beach. People can go snorkeling themselve or, i havent tried it, but there is a company Butterfly Diving, which arranges trips by boat around Tucepi (Hvar, Brac, Podgoda, Baska Voda). The instructors lead you and show you how to dive if you dont have any experience yet. The trips are for the whole day. I dont know the price.