My sister is the DD2 on this situation. When she had her first child, the first grandchild, she used her as a pawn in a stupid game that my parents fell for. My parents babysat her overnight, so my sister could get a break, when she was 2 weeks old. That started a routine of her going to my parents' every weekend for around 7yrs. My mum, also, had her every afternoon so my sister could work.
She was taken on holidays, weekends away, shopping trips, theme parks etc and once her brothers were born they went too.
My DH was in the forces so we lived an hour away when we initially had our 2 children. If I had an emergency there was always a reason why they couldn't help, even when I was in labour with DS2.
Fast forward a few years and I did confront my mother about all the holidays etc and was told to grow up and history was rewritten. From that day on they used to lie about the holidays but my middle nephew was shit at keeping secrets so it all used to come out.
11yrs ago I was having major surgery, again, so asked my mum if she'd come to my home for a couple of nights just to oversee my kids (they were teens then) because I was going to be in hospital 50miles away. She was busy. Well it came out she was taking my niece, her son, and my 2 nephews on a sunshine holiday.
We had a massive row over that. She reckons she's always been fair and treated them all the same, when in reality she's never even bought my kids a packet of sweets when it wasn't their birthday or took them to the park.
I've seen her once since then, my kids, through choice haven't seen her at all. They won't go to either of my parents funeral either, simply citing "you reap what you sow."
Sorry about the long post, but these things are never about money, it's about time and relationships.