1. SINK OR FLOAT
Bring a variety of everyday items into the bath with your child. Try sponges, balls, favorite plastic toys, plastic building blocks, toy boats, and plastic dinosaurs. Have your child hold the item and ask, "Do you think it will sink or float?" Try holding two items and guessing which of the two will float and which will sink. (Small children tend to think very heavy objects sink and light objects float.) Then, test to see!
Try floating a washcloth on the surface of the water and placing objects on top of it. Will it sink? Will it float? How many items can your child place inside a plastic bowl before it sinks?
2. WATER DISPLACEMENT
Before putting your child in the bath, mark the waterline with a bath crayon (available at toy stores). Show your child how the water line goes up when you put him or her into the bath. Mark that line, too. If you are bathing with your child, make one mark for your child and one for you. Explain how heavier things displace more water than lighter things. (More water has to move out of the way for heavier things than for lighter things.)
3. MAKE MAGIC COLORS
Add a few drops of food color to ice-cube trays, add water, and freeze. While your child plays in the tub, she can drop in an ice cube and watch as the water changes color. Talk about how the dark ice cube turns the water a light color, and then try dropping two different colored ice cubes into the water and guessing what color it will make.
4. BATHTUB BAKING
Bring a selection of plastic measuring cups and spoons into the bath with your child. Kids enjoy pouring water from one cup to the next and using smaller cups to fill larger ones. How many 1/4-cup containers will fill up a cup? How many tablespoons fill a cup? Suggest pretending to bake something in the tub--it will help your child explore the basics of measuring and is an unexpected bath-time game.
5. WATER SPOUTS
Take a clean plastic cup (yogurt cups work well) and poke a small hole in the bottom. Try several cups with holes of different sizes. Show kids how to push the cup into the water to make water spout up into the cup through the hole. When they pull the cup out of the water, kids will enjoy watching the water drain out. Now turn the cup upside down and try pushing it into the water. Place your hand over the cup to feel the air escaping. Try pushing a cup into the water that has no hole in it.