Do you say something to them?
I'm sorry. That stinks that they blow off the kids' birthdays, especially since they are godparents. I've got some relatives that forget our kids' birthdays too, but it's fine. We do our small family celebrations, and that's really all that matters. Anything else is just icing on the cake. I hope Nick had a great birthday despite all this.
My dad is really, really bad about remembering dates so he asked for me to set up a shared family calendar for all of us. We use Cozi.com. Each family has their own color code for events, and everyone can log in and add/remove/modify their goings on. We've been using it for about three months now, and it's been helping everyone stay on top of what's going on with everyone else (t-ball games, recitals, birthdays, anniversaries, etc.). I don't know if something like this would help, but I just wanted to throw it out there because it really does seem to be working for us.
Last year Kaiden was left out while everyone else got a birthday present. We didn't even get a phone call, card or anything. It also bugs me a little that Kaiden has never had a birthday party with family, even though he's only 3. Anyway, I let go for awhile until it just really bugged me when Kyla got a more expensive present for her birthday. I finally spoke up and said if you want to get something for one kid, please don't leave the other one out and that I'd rather neither of them get anything than only buying for one. Needless to say, he got a much nicer gift for his next birthday lol. I'm glad I spoke up though instead of feeling resentful. Sometimes I just feel like since he was born here that he's the forgotten grandchild.
BTW, I think your SIL and mine should get together and make each other's lives miserable instead of ours for a change. I keep telling myself that just because we're related does NOT mean that we have to be friends.