Get sponsors, and run a road race, particularily a marathon.
My son’s school go to Companies like Baskin Robbins. You can look up numerous companies on-line find one your community might buy the most from.
I was thinking about a car wash…good for upper grades or hs, but why not a primary school? It would be a good time to meet each other and to contribute time to a group effort rather than $$$ directly.
I have sponsered several. All with good to moderate success…just pick a cooperating day from the weather.
You need a parking lot with a water supply and hose. Most schools have that. A clothes dryer has proven very helpful in quick-drying old towels that were donated beforehand.