Here is a simple, colorful, brief video explaining for children of what Pentecost is:
Building Faith also has some object lesson and children sermon suggestions for Pentecost that would work in class or at home in this blog posting by Alison Juurinen: Sharing the Pentecost Story with Video & Activities:
"Pentecost has the potential to be one of the most ridiculously fun days of the entire liturgical year, in my opinion. It’s not every weekend you get to launch things into the air at church, but if you’re going to do it, by golly this is the time. And fun flying objects are a great way to do intergenerational ministry – the kids bring their apparently limitless energy and enthusiasm, and somehow the adults always seem to catch a little of it too."