Take a container of small toys, like matchbox cars, or a collection of sea shells or rocks, and create categories. Have your child sort them by type, color, or size. For example, if you sort by color, you can draw a bar graph and show which color is the most popular. Your child can create the bar graph on the floor using tape and lining up the similar items. This is a very visual way to illustrate the graph. Then you can ask comparative questions about the data they have created: How many more red cars than yellow cars? What is the difference between the number of black cars and green cars?
Have fun with math!