Balls or packing peanuts
Nerf balls and toys
plastic sheet (at least double the size of the pool)
Let's make it
Put the pool on the plastic sheet. Fill the pool with balls or peanuts. Throw in Nerf toys. Add kids and play. When done lift the pool with remaining stuff off the sheet. Pick up the corners of the sheet and pour stuff back in the pool. Place sheet down again. Sweep stray stuff back on sheet, then pour in pool. Put sheet down again. Put filled pool on sheet for more fun.