I'm the daughter. My parents did a lot of childcare for me in the kids first few years. I can't remember what we discussed beforehand but I do think having the conversation about expectations and costs is really important. Plenty of posts on here resenting GP's who don't help but helping brings its own issues.
GP's wouldn't take anything for looking after mine but I bought and delivered all nappies, wipes, nappy sacks, food, snacks, bottles and other bits and bobs that would be needed at theirs as well as leaving extra clothes etc for accidents or mess. GP's wanted to buy toys, playmate etc themselves to keep in their house for kids. They bought a stroller for their house and we bought extra car seats that were isofixed into their car.
I didn't want to book too many activities for them to have to get to but mum took DD to a little music/ dance class, gymnastics and the library for kids groups. I paid the first two direct.
Someone else I know had 50/50 childcare split between mum and mil. She paid £600 to mum and mil didn't want/ need anything.
I'm of the mind that my parents were doing me a massive favour and didn't leave any rules etc for them to follow. Did have to bite tongue sometimes eg when my Dad would say they didn't eat any dinner so he gave them some ice cream.
My mums days were longer and more tiring than mine as I had commute either side of work before collecting. My mum wouldn't tell me just how tired she was but we did realise and we later did 50/50 with paid childcare. My mum wanted to be able to have a chat at the end of day before I took kids home but because of long commute I couldn't come in or stay on doorstep as getting straight home it was nearly 7 and we needed to sort our dinner and kids bath and bedtime.
I would ask what the kids had eaten etc but sometimes my mum would take it as checking on her when I just wanted to know if and what they'd eaten or if they had refused food etc