You can do this inside or outside, but be sure you are supervising any water play, even if there are only a few inches in the container.
What to do
Fill a large plastic bowl or tire tube lined with plastic.
Sail a boat made out of paper or a coconut shell for pirate fun.
Find things that sink and that float - this is a little science experiment.
Use a feather, cork, stone, acorn, leaf, rubber ball and anything else your child finds.
Ask before she or he drops it into the water whether it will sink or float.
Ask why it sinks and why it floats.