I did it yesturday.

I only attempted it with my 3 year old and not with the 15 month old. It is messy, but he had a ton of fun and played with it for at least half an hour. He had the funniest look on his face trying to figure it all out.

I let him do the mixing so he could see the different textures come together and change.

It really wasn't that hard to clean up either. It came out of everything with a few wipes.