These experiments study the effect of such leavening agents as baking powder and baking soda. Have your kids bake identical batches of cookies, one with baking soda and one with baking powder, and evaluate them on flavor, coloration and rise. The same experiment works with a cake. The greater complexity of cake opens more doors for experimentation. Bake several identical cakes with increasing amounts of soda to determine what quantity is optimal. Alternatively, experiment by adding various ingredients to a cake to establish which are acidic enough to activate the soda, provide rise and neutralize its chemical flavor.
Instruct your kids to bake identical cakes or cookies with cake flour, all-purpose flour and bread flour. Sample each one and discuss the differences caused by the gluten in the flour. Try baking cookies and cakes with other flours, such as oat or barley flour. Have the kids record their effect on flavor and texture. Experiment with combining oat flour and all-purpose flour in differing proportions and examine the effect. If your kids are old enough, bring in an inexpensive coffee grinder and some whole grains to have them grind their own flour.
Sweeteners have sharply different characteristics. These affect the end quality of the baked goods in many ways, providing more fodder for experimentation. For example, try baking cookies with corn syrup in place of the sugar and have your kids evaluate them. Substitute brown sugar for the white sugar in a cake or cookies and see what difference it makes in their texture, flavor and rise. Compare an artificial sweetener head-to-head with sugar.
The effect of aging on baked goods is another source of experiments. Save samples from your experiments with sweeteners and track their characteristics for a week or two. Some sweeteners attract moisture and will keep cake moist or cookies soft for longer than other sweeteners. Another experiment is the mold test to monitor foods as they age and track mold development. Have your kids bake a cake from scratch and one from a commercial boxed mix. See how their texture changes as they age and encourage the kids to speculate about which one will mold more quickly.