I can remember doing this in school when I was a child, and I've used this activity as a teacher multiple times. The boys absolutely loved it.
Henry got more shaving cream in his hair than anywhere else, but he was sure excited. I actually got Nick to play a game with me where we drew letters and numbers in the shaving cream and guessed what they were.
We will be playing with shaving cream again. If you smear it around long enough, it just disappears. Your arms and hands get nice and soft, and everything smells good. Henry, however, did need his hair washed.