I went as far as suggesting no more gifts for anyone. I suggested we just get together and just have fun. Nope. They were not going to go for that.
I'm the only one with young children and I really don't like them getting so many gifts. I've suggested making a donation in their name to a charity, but they just think I'm crazy. When my sisters ask my kids what they want, their answer is, nothing. My kids are just not into "stuff".
Seriously, put your foot down. Tell them flat out that you aren't participating anymore. Tell them to either keep the receipt for the gifts they buy your children or they will be donated to charity or children's hospital unit. Mean it and stick to it. Tell them your children are fortunate already to have everything need and the only thing they want or need is the pleasure of the company and the happy family memories.