I don't want to distract you with last minute ideas...but you asked...

I once listened to a presentation (the topic isn't important, but it did involve children) where the presenter used Peanuts cartoons on the overhead projector to illustrate various ideas. It was one of the best presentations I ever heard.

I also participated in a workshop where I ended up playing the piano for an afterhours get-together where everyone was obsessed with the song "Happiness" from "You're a Good Man Charlie Brown."

This song is very catchy and has several lines appropriate to children and music:

Happiness is playing the drum in your own school band.

Happiness is singing together when day is through.

I can't find the midi on the 'net...suspect copyright issues...but did find a short clip here.

Once I used a cartoon of Schroeder and Snoopy dancing on the piano for the program cover in a children's piano recital. That probably has copyright issues too!

Good luck on your presentation!