We did a clothes race when I worked at a daycare one summer.
Before the race, student organizers bring discarded clean clothes - oversized jackets, hats, pants etc. - from family.
On the day before the race, arrange 3 clothes piles (pants, top, hat, etc.) for contestants.
Place cones where runners will turn & head back to line.
Place pre-arranged clothes piles at 3 stations.
The first persons in each team put on everything in clothes pile.
At the whistle, they run down to the cones and back.
Take off clothes for the next runners.
Do this until everyone has gone.