My parents were always clear that they would not provide full-time childcare but we're happy to help out, and I fully agreed with that. They retired around the time the GCs were born, and my sister and I both wanted them to enjoy their retirement, having both worked since leaving school at 16.
They both have hobbies, enjoy travelling, and have friends round; they do a day's childcare for each of us (my sister and I - all the kids are at school, so it's just picking them up and being there for a couple of hours) and they're happy to step in if there's an emergency, and they usually have each set of GCs for a night during school holidays. Everyone's happy.
On the other hand, when SIL had kids, she expected MIL to mind them full time as soon as she went back to work - so MIL drive to her house for 6.30am, waited till school time and dropped off whichever ones were in school, drove home with the pre-schoolers, then went back to do the school run (which was sometimes 2 runs when they got out at different times). Then she'd do homeworks and get them fed and changed, ready to be collected. She also did things like going to the post office to collect missed parcels, sorting out tradesmen who'd come to do stuff to SIL's house - all those little things that add up to quite a bit of hassle if you have a toddler under your arm. She died at just 60, and DH is fairly sure that the childcare was a big factor because she was just permanently exhausted, and never got a break. But they had the attitude that "family help each other", which mainly seemed to translate to "mum will do everything".