You will need:
A child friendly darts kit (they do exist) we like this giant grass one from AMAZON
… and this fence worthy ball version again from AMAZON
If you don’t have time to order a set, create your own using string (to create target circles) and balls (as the “darts”)
Paper and pen to keep scores
Small Prizes for the winners (think something for everyone – best archer, most flamboyant, most determined).