My DH's father acts completely different around my Skids than my daughter. I always just chalked it up to the fact that he has known them all of their lives, and my daughter came into his life later, she is not biologically related, the connection is just tougher. Now, my daughter is 8, and actually seems to understand somewhat. She doesn't expect equal treatment, and therefore, is not disappointed. Though the disparity is not as pronounced as yours seems to be. I think, if your children are affected negatively by this, you have go to talk to the inlaws. I think risking a fight with them is far less harmful than your children continuing to endure the unfair situation. I would start by telling your inlaws that you understand they feel closer to their bilogical grandkids, but that when it comes to children, they do not understand the difference, and that you would appreciate it if they are not going to be able to make a big deal out of ALL of the kids's birthdays, that they just leave the parties to the parents. That is not overstepping your bounds, and it is not asking too much. Most kids do not get parties from GPs, so no big deal if your skids don't either. I would put the kids' feelings above the inlaws.

Best of luck!

I grew up with a step-father that adopted us after "we" were married a few years. (my bio dad died when i was very small) however, dad's parents and siblings never even learned our names properly, birthdates, gave christmas gifts or anything, even when we visited at the holidays.

we knew that they did stuff for and with our cousins and it hurt for a while until we just stopped spending time with them. the older i got the angrier i got and i could really care less about his family now. i don't even think of them as being related to me - they are related to him. they are strangers to me, which is sad, but kudos to my mom for not forcing us to spend time with people that didn't care for us since we weren't his bio-kids.

LCooper gave good advise, e.g., about leaving the parties up to the parents if MIL is unwilling to acknowledge how this favoritism is perceived by the kids and unwilling to change it. And perhaps the best way to open this conversation is to call the MIL and remind her of the upcoming birthday and what are her plans for this pizza party.

My mom treats my SD differently AND I've talked to her about it. So far, only my DH and I notice the extra gifts, attention and general interest in MY kids versus my SK. I know a lot of it has to do with my mom and her own issues but some has to do with the connection she's had with the kids over time. She also gets to see my girls more just due to visitation so the relationship with SD can never really catch up. Sometimes she is just negative about them because she wasn't a SM, and doesn't "get it". In her Christmas newsletter last year she went on and on about my kids, and didn't even name my SD by name, just called them "the other ones". It was really hurtful for everyone and she never even considered it. (clearly we talked at LENGTH about that one!) On the flip side, MY SM and Dad completely get the importance of balance and equality where possible, because they lived it.

We've made ground rules however. A gift for one equals a gift for all. WE organize birthday parties to ensure fairness. It's not something that she tries to do, or even knows she's doing, but it's been a process over the last few years.

I found my MIL actually trying to find fault with my boys because she couldn't handle the fact that they were respectful and nice...qualities her Granddaughter is really lacking. I had a hell of a time putting up with it on her last visit. I just moved back from it and took the I feel sorry for the whole lot of them, they don't share a real love. I am extremely proud of my children when their step GP come to visit. They are on their best behavior and it drives my MIL CRAZY...she is just another person who inables my SD's rotten behavior...
My family have always treated SD as one of the family.
good for us...they suck!!!