My son's birthday is next weekend and I didn't invite my kids. Same thing, I don't want to blur the lines. Personally, I don't think it's a good idea to mingle with clients outside of the daycare because then they think they have an "in" and try to take advantage of little things and it eventually becomes an issue - well, it did for me anyways. I think you're doing the right thing by not going but that's JMO