Hi CESCHOOL,
Your back-to-school event should be about connecting with parents in a way works for your group. Setting up a table is a good idea. Your main goal is to be welcoming and let parents know about the work your group does. Will your event be part of the school's back-to-school night or will you do a separate event? If you are part of the school's night, that might dictate how much you do. For instance, if the administration is giving an overview, you might want to see if you can do a quick presentation on the group.
Back-to-School section: https:/classic.ptotoday.com//filesharing/category/97-back-to-school