If you want to... not a matter of 'supposed' to, I don't think. I never heard of any order that addresses kids' social events.
My kids' mom never tells me about that stuff, I don't really tell her either. That's another big reason I feel like it's important to get to know the other parents and teachers in the kids' classes - so I know what's going on for all that stuff, without having to ask kids' mom.
Early in our separation I remember a birthday party for the kid's friend I found out about and told her I was going. She got mad and told me I couldn't go, we weren't together anymore. I said of course we aren't together but what does that have to do with either of us going to a party? She gossiped with all the airhead moms and I hung out with my kids and the family hosting the party. I was the one who ended up staying after, helping to clean up and joining the after-barbeque and watching the boxing match that night. Still good friends with their family, kids hang out. It was fun.
Only chicky dudes have signatures on internet forums.