Did you bring anything to the pool that can float? What about an empty soda can or some aluminum foil? Did you bring any floaty toys? Put each of the items in the water and see how they float. Can you rework the materials so they sink? What can you put on them or in them and still have them float?
Questions to ask:
How much of the item is under the water and how much is above water? (Things that float generally have more air, which is less dense than water).
What were the shapes of the things that float? Does the shape matter? (The shape might not matter, but how much surface there is to displace the water does. For example, a ball of aluminum foil won’t float, but a flat piece of aluminum with turned-up edges will).
How much weight can your floaty toy carry and not sink? (When the weight (mass) of the object is greater than the amount of water it is displacing, it will sink).