I taught Elem. for a few years in between band gigs. Once I got comfortable with what I was doing, I approached my teaching with "what did I wish my kids already knew" It came down to fluency with regards to note reading and basic counting skills. The only other thing I would add is getting them in the habit of caring for whatever instruments you may use. Getting them to understand and appreciate their equipment (as much as an elementary student can) will definitely go a long way.
Last, don't underestimate what they are capable of understanding. When our band director came to observe me and meet me, she saw me teaching fairly complex rhythms to little ones that they were counting and drumming, we became best friends. Good luck and keep those little ones busy.