For Family Home Evening a few weeks ago, we put Alex and Edison in the bathtub. They were confused. Sam started telling them the story from the Book of Mormon about the Brother of Jared building boats and then seeing the finger of the Lord touch the stones to light the stones so they wouldn't have to cross the waters in darkness. I turned off the light and then we "touched" the glow sticks so they would light up.
I don't know how much of the story they understood but they loved playing in the bathtub with the lights off and asked for the glow sticks for days and days after that night. Alex really loves Family Home Evening and asks for it all nights of the week.