My parents live 10 mins from us and are retired. When we had kids they said they wouldn't provide regular childcare and that's absolutely fine.
However they will often offer to have the kids ad-hoc during the week to give me a break (we have a toddler and baby) but they'll offer at the last minute or they'll keep changing the time that they're coming or they'll say they'll have them and then make other plans and cancel.
I find it really annoying because what should be a lovely thing for them to do to give me a break feels like actually i can't rely on it to get a break but i don't know if I'm being unreasonable and i should just be grateful for any help i get.