I'm a childminder and I charge for the parents holidays, but not mine. I take five weeks off per year, I book them in at the start of the year to give parents plenty of notice and I try space them out a bit. I don't charge for these five weeks but if, for example, a parent decided to take a weeks holiday and I was supposed to have their child that week then I do still charge. This is in my contracts and is standard where I live. I don't charge for bank holidays but all of the other minders in the area do, even though they don't work them. From next year I'm planning to be open on bank holidays, except Christmas, as I've had queries about offering these days so if the bank holiday falls on a day I'd normally have that child and the parent keeps them instead then they'd be charged.
If I need to take emergency time off, e.g., sickness, then I don't charge the parents but if their child is off sick then I still charge (this covers me in the event that I catch whatever the child has had and then have to take time off).
I don't have anyone who is term time only right now but if I did then I wouldn't charge them for school holidays. In effect not having that child in the school holidays means I have a free space foe the duration of the holiday and there is always someone who needs holiday only care that can fill that space.
All childminders looking after children under the age of five need to be following the EYFS. He's three years old, they should be supporting his early education with appropriate activities, keeping a learning journal for him, and carrying out observations to help build on his skills and interests. It's part of the national curriculum and they are failing OFSTED registration requirements if they are not delivering this. Messy play is part of it, if they aren't doing it at home they should be going somewhere where it's provided (for part of our messy play we go to a weekly craft-based playgroup).
If you have doubts about what they're doing with him then ask to see his learning journal, their latest observations, and for details on where he is within the EYFS framework. Ask how he is progressing and where he sits now as compared to where he was when he first started. If they're rubbish, they won't be able to give you the information because they won't have it.
If you have any misgivings about the person looking after your child, you need to find a new provider.