This is not a new concept. My mother in law has done it forever with kids she watched and my boys have done it with her as well. I wanted to pass on the fun in case you've never done it!
What you need:
Shaving cream, pudding, whipped cream (may want to use edible for younger kids)
What you might want:
Plastic toys that can be washed off (animals, LEGOS, action figures), cookie sheet, plastic table cloth, foil, trash bag
If you are doing this on your counter you may not need a protective covering. We were doing it on our porous dining table so I layed down what I had on hand (a trash bag) and secured it with some tape. Squirt on some shaving cream (we took Dad's shh!) pudding, whipped cream and just have fun! Plan on a bath afterwards if you use edible sticky items.
Still gets smiles from my 10 year old!
For clean up I just folded up the trash bag and he rinsed himself off
Tip: To keep the fun lasting longer introduce items slowly. Let them play with just their hands first, when that fun slows down add a toy or two, then a car or a ball etc. If you throw everything out at once the "fun" will wear off faster.
When they were younger we'd just throw them in the tub or in the summer hosed them off outside!