My mum looks after our DS's pretty much 8-30 - 5.30 during the week. Takes them to school, clubs etc. And she will also babysit on weekends and evenings for us fairly regularly.
She's very fit and active and she offered to do it, so that I could return to work full time. Having my mum do the childcare is the next best thing to me doing it and as we need two incomes at the moment it really helps us. My mum loves doing it and feels she's a much better grand parent than parent as she's got more time and patience. We do pay her and although I don't expect her to do housework etc, she does. If the DS's are busy playing she'd rather put some washing on than sit in front of TV, as that's what she's like.
I do know how lucky I am I and really appreciate everything she does. while she thinks it lovely to be so involved in our and DS's lives. So we both win. My DS's also love my GP's and love spending time with them. She knows that DH and I work really hard, so she offers to babysit so we can go out together sometimes.
I always make sure to take time off work, when I can, if there's a special school event or if DS's are ill etc. I also encourage my parents to take days off and holidays etc so my mum gets a break from time to time and also,so that I can enjoy doing the normal mum role too.
It is an unwritten agreement that when my parents get really old, DH and I will look after them for as long as possible, rather than stick them in a home. We see it as an extended family working to help each other when it's needed.
It works well for us and it had never occurred to me that anyone would think it was anything other than a good thing.
While I do appreciate that expecting your parents to bring up DC instead of you would be taking advantage, where should the line be drawn?