This sounds like an informal open house? Did you/do you have to RSVP? It sounds like they're doing something nice for the kids, parents, teachers, staff. Show up or not. If you're really not interested in going, don't. If you think you'd like to connect with people, maybe meet your kid's parents and friends, sounds good too. It doesn't sound like something you have to stay at for very long, and if it's just not fun, you can be on your way. If you choose to go, this doesn't obligate you to attend all future events. It's not rude to not go. I'm sure plenty of families have made plans for after graduation. Thank them for the invitation but you will be unable to attend and be done with it.