The concept behind this is too advanced for A, but it is a neat visual.
Take wooden toothpicks & break in half, but not apart. Place then so their center (folded) parts touch. Drip a little water at a time on the center & watch the toothpicks move apart.
(This works because the the water travels through the toothpicks using capillary action)
SKILLS: Observation, Fine Motor Skills, Water Properties