You can make a water rocket using an old plastic soda bottle, a cork and a basketball pump. Get a cork that fits snugly in the soda bottle. Cork it and push the pump needle through the cork. Stand the bottle upside down, outdoors, and pump until the cork pops out and the bottle shoots into the air. They can go up 30 - 40 feet.
Most children like to experiment with lenses and magnets.
Prisms are fun and they also demonstrate some basic facts about the nature of light. Colored gels for flashlights can be fun, too. You can grow a carrot or sweet potato top in a cup of water. You can grow real grass for your Easter basket instead of the plastic stuff. If you start a few weeks before Easter, you'll have a luxurious crop of grass for your Easter eggs.