SS is going to be 6. The CO says that both parents share his actual birthday. Historically, since SS's birthday has fallen on BM's days, BM has invited DH and me over for dinner and DH and I have picked up SS from his mom's house for an hour or so for breakfast. This year, we will be picking up SS for breakfast at 8am and dropping him back off at noon. We requested this arrangement prior to being made aware of BM's plans for his birthday, which she formulated after we requested the time. BM will be having his big party for her side of the family that day after we drop him and some of his friends are sleeping over the night before into the day of the party. I'm just wondering how fair it is to SS to come to pick him up in the middle of spending time with friends who slept over and then bringing him back. Last year when we took him to breakfast, he kept asking when he was going back to BM's because she scheduled his big kid's party for right after. I think it's nice his mom has planned things to celebrate his birthday to make it special for him, but by the same token, I would like to feel like we have some dedicated time carved out for us to spend with him as well that isn't filled with "when do I go back to Mommy's?" We already don't really "share" his birthday because we only spend a fraction of the day with him, and we only have him EO weekend. When he will be with us on our day in future years, we likely won't schedule any parties or anything on his actual birthday and will keep it low key. I'm curious how you guys do birthdays and what has worked/hasn't worked when it comes to "sharing." TIA!

Re: Handling birthdays
DH doesn't have anything in the CO regarding K's birthday. Last year it landed on BM's day, so we celebrated with her the next day. This year it's on our day so we'll do a big dinner and stuff after school. The weekend before K's birthday (or the weekend of, depending on how the weekends in the month land) we do a small gathering for K and a few of her friends, and BM does her own party when K is with her.
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There are a lot of shortfalls of the CO - at this point we don't have the cash flow to open it all back up to put a lot more specifics in.
I would say the evening might work except it's on a Sunday this year so depending when the party ends, it might be late/short period of time.
I think BM's poor planning is going to bite her in the butt.
You are scheduled to pick up SS at 8 am - so what time are the guests going to go home, and is she going to be entertaining a bunch of 6 yo while she waits for their parents to pick them up?
Also, because of the sleepover the night before, she is going to have one cranky / sleepy 6 yo at her family party.
However, I don't think it's 100% fair that you are criticizing BM. Since SS's birthday falls ON the weekend, and you have him EOWE, she has limited opportunity to throw a sleepover if that is what her son wants. Yes, she could have scheduled Friday night, but for whatever reason, that did not work. And just because you envision having a low-key birthday doesn't mean that is what BM has to do, or even what SS wants.
You seem to have a decent relationship with BM (I'm guessing b/c of you can sit down and share a meal with no drama!), can you talk about your concerns? Is it going to matter in the next few years, when SS has a birthday in the middle of the week? I think some of this may be a communication and expectation problem, not a selfish BM problem.
I agree that taking the kids to IHOP or someplace similar may be a great idea!