Grannytomany - think you have hit the nail on the head - My best friend (sadly dead now these past ten years), often complained to me that she had no friends. I did point out to her that one of the reasons was that she let people (including me) down often with arrangements if one of her children clicked their fingers at the last moment for childminding.
She desperately wanted to be needed by her children and they took advantage (do not think they realised it). I did tell her that to say 'No' occasionally - particularly when she did have other arrangements would actually earn their respect, but she could never bring herself to do this.
Even when she came with me on a weeks holiday, she returned back after 48 hours as one of them called to say she needed her for baby sitting!!!! When she visited one of her children in Australia, she complained to me, that they had not gone anywhere during her three weeks there, and had been given the new baby to hold almost as soon as she arrived. She said that this was done as if they were bestowing a great honour on her. But, she only said these things to me, NEVER to her children.
I made it very clear to my AC from the start that I have done my job of bringing them up, and my day for that is over. Whereas, I am happy - where possible to help out in any emergency, I am not in the business of child-minding any more. Did help once or twice a week with nearby daughter who became a single parent very early on - but that was it. When I visit my children, it is THEM I am visiting, the g.children are almost incidental - and they all appreciate that my own children are first for me.
Love my g.kids, obviously, but as I only see them occasionally, can be the 'Spoiling Grandma' on those occasions