If you're lucky this will occupy the kids (and adults) for hours.
All you need is a can of shaving foam and something to colour it with. We used watercolours (in tubes) but you could also use tempera paints.
Just shake and spray the foam and top with splats of colour. Hayley doesn't like to get her hands dirty so she used various utensils to push the foam around with. Limey was a little more easy going and ended up with a foam hat on his head at one point.
It's fun to see what colours develop as you play.
Although it looks like a big mess, it is super easy to clean up, especially if you put paper on the table first.