Childcare

Pay for the childminder.
You don't want someone who resents your children looking after them.

You're paying your mum in coffee and snacks so why not pay a professional who enjoys looking after them instead.

I've never used family for childcare as it just gets messy

I would just pay the extra for childcare to be honest x

Yes I’ve had a very similar experience with my first two children. I’ve just had my third and I’ve told my mum I will be using nursery 3 days per week opposed to 2 days nursery and 1 day with my mum

She probably didn’t realise how tiring it was and also how much of a tie it is. She clearly loves them as she wouldn’t have offered however there’s a difference between being childcare and being a grandparent. I imagine your second child will be off to nursery soon anyway which will make it easier on your mum. I assume you also thank her for looking after your children one day a week and don’t make her feel like she’s being taken advantage of either.
My brother had my mum babysit my nephew one day a week until he started school and now he’s moaning as my mum needs care and he lives near her. I also had my nephew one day a week. He had two days free childcare for four years so find it hard to sympathise with him although he forgets that!
I’m sure the occasional coffee still works out cheaper than a childminder for two children even if one is in school.