ProudGranny, reading this really hit home with me and made me hurt for you. My grandkids spend halftime with their Mom and half with my son. It is a constant struggle making sure things I get for them stay at my sons' because I know they will be lost if they go to their Mom's. I can't tell you how many cute outfits I've bought for my granddaughter and never seen her wear them because they end up at her mom's. Their mother is not mean by any stretch but she just doesn't think.
I cross-stitched a Christmas stocking for my grandson the year he was born, and it took me ALL year to do it. That stocking has disappeared because they always spend Christmas morning with their mom. I was just sick about it for a few weeks but I've told myself it's just a stocking.
Apparently, this is a common problem for us grandma's who have grandkids that spend time in two homes. Ah, well, as with you, my grandkids and I do have that special bond that can't be broken. That is so much more important.