No matter who actually sets up or tears them down, the COACH and TEAM MANAGER are responsible for the goals at all times, and for ensuring the setup/teardown procedures are followed. Be sure to review procedures with assistant coaches and parents (including opponents' apparents if they are assisting) before having them assist with setup or teardown.
Setting goals up correctly is critical to player safety. READ THIS!
Also, be sure to zip up the goal bags after setup, with the hammer and any extra parts inside; then lay on the back edge of the net, zipper side down. This helps minimize the risk of parts being stolen, and of morning dew or rain water (or unexpected sprinkler water) getting into the bags.