Beavers can create their own car track using junk
One toy car, lots of junk, sellotape/glue, scissors
Split your colony into teams (3 or 4 beavers roughly in each team), give them 30 min to build/design a track that a toy car can drive along. You can give points to the teams who have the nicest looking, fastest, highest track and also to the teams that worked best together etc. If you have them, put one YL in each team to help too. At the end take a toy car and let the children test out their track.