DD(3) has recently started getting a lot of birthday party invitations from other children at nursery, mostly from children we don't know but she does IYSWIM. Some of them are quite expensive options like soft play parties. As it turns out, all but one so far have clashed with other things, so we have rsvp'd "no, but thank you very much for the invitation".
We are very unlikely to have this kind of 'extended friends' party when her birthday rolls around, partly due to cost and partly because we have a huge family so tend to have a party at home with family and close friends.
So, WIBU to accept invitations for her, knowing that we probably won't reciprocate? DD is sometimes a bit oblivious, on occasion doesn't even know who the party child is when I ask her, so probably wouldn't be that bothered if we declined, if that makes any difference.