Experiment 1:
You can simply use ice and float it on water to show kid that how buoyancy force is getting the ice partly submerged in water.
Experiment 2:
Mix Baking soda with acetic acid to show kid the vigrous reaction, Carbon diaoxide as a biproduct.
Experiment 3:
Can use two magnets to make kid learn about the concept of Poles, same pole repel each other and opposite poles attract each other.
