Can They Do This

So this question is more legal but I don't know where else to ask. I'm currently struggling with a custody battle. I was given weekends, (Fri-Sun) and Monday and Wednesday, and Holidays. Ex gets the rest. I wanted to take my child Trick or Treating. They are refusing. Instead, they want to let the uncle and his girlfriend take him. I don't know if Halloween is even a legal Holiday. They are trying to use the excuse of "it's a school night" but isn't the uncle taking him out on that night the same thing? I don't think that's fair. Can someone not in the custody proceedings even take a child on outings? Or am I just being selfish? Should I just "let it go" or am I justified in fighting him on this?