My DPs regularly treat my DSis and family to days out, even the odd holiday abroad etc. as they can't afford it and don't want the GC missing out 
Now whilst myself and DH (no children) are not invited (not too bothered about this) I was slightly miffed when I received a call from my DF asking me to book their latest outing and pay the initial outlay (will get money back). If we had been invited to go along I wouldn't have minded but yet again we weren't asked.
AIBU to be slightly miffed at this.