I'm honestly not sure if me/DP are being unreasonable here or if, as I feel right now, DSC's mother is being difficult for no reason.
My DSS (7) is very shy and quiet. He finds it hard to make new friends and doesn't really "like" much out of school.
We wanted to find him something to do out of school so he had a hobby. I found a local Beavers group and added him to the waiting list a year ago. He was offered a place in September. DO spoke to his ex before accepting the place, 50:50 residency means every other week he'd be with his mum so he needed to agree. She did. She agreed it'd be great for him socially and his confidence and said she'd take him as long as we paid for his uniform and the termly fees would alternate who pays them. All seemed good.
We bought his uniform and he started in September. He absolutely loves it. He asks every day if today is Beavers day, so proud of his uniform, runs all the way there, goes on and on about it all week - you get the idea. It's one hour a week.
In November, he was with his mum one week and we had a call from the Beavers leader to say he hadn't been collected. They had called his mum and she wasn't answering mobile or house phone. All the kids had gone and the leader was the last one there, she said she had to leave (Beavers had I used 40mins ago). So I walked there and collected him, very confused as to why he hadn't been picked up. I got back and called his mum. She answered and said she was on her way now and had been delayed. I explained he was with me and she drove to our house and was very rude at the door in front of the children.
She then decided he could no longer go during "her" time as she says she doesn't agree that I should have collected him. He's absolutely devastated. He's still going when with us but he's missing a lot and he's finding it hard to do the work towards his badges (which he's obsessed with doing). Twice now though she has agreed to is collecting him from school on Beavers day when he's due to be with her and us take him and take him to school the next day.
He has asked if he can come here like that every week so he can do Beavers. She refuses. He's really annoyed and angry and hasn't stopped going on about it. DP has tried explaining to her he will reliably have him on those days and how much it will benefit him but she has just said it's "her" time and her choice.
Argh. He's cried in bed tonight and asked me to make his mum let him go. 
He's one of those sweet kids who never asks for anything, never moans for sweets, never asks for things at the shop, never has a Xmas list etc. He's not particularly excited or bothered about anything but this.
I just think surely a little flexibility is needed, the DSC are getting older and they have needs and wants that aren't covered by the rigid Court Order of mum's night and dad's night. There's a provision in the order for "alternative agreed arrangements" so it's easily agreed.
What do other people do?