Am I being unreasonable?

You have a good relationship and get to feed the family once a week. Many Grans on here would love that. I do something similar with my granddaughters and do it happily. After school the children are happier in their home and if we do something messy, like baking, the mess is in their house.
Count your blessings.

I don’t understand but it just makes a mess in my house
Surely it’s the same mess in their house as it is in yours.
That’s assuming you clear up after cooking in their house.

I too used to have my grandkids more often in my own house and preferred that because I could be getting on with something whilst looking after them or inbetween games When I had them at their house I felt I was twiddling my thumbs.
I would expect to feed them with my own money, blimey it’s only once a week, not every day wellbeck. If you can’t buy your grabdkids a tea once a week that’s poor do s
About the popping in I don’t think people do ‘pop in’ so much now. Why not invite them all to a Sunday lunch or similar or invite them over for a fish and chip supper or takeaway if you don’t want to cook or anything really but if you’re waiting for a pop in you might wait a long time, they can’t read your mind
None of my kids are pop in people and I’m glad they re not I like to be prepared

What Yorklady says. I preferred to bring them to my house. I liked to prepare the food in my kitchen. Very often , my daughter used to do sone shopping, but tbh it wasn’t a big deal. I didn’t mind doing that, but used to smile when little granddaughter preferred her other Nan’s cooking. I would say, well D , when you’re in Nan’s house, you must eat what Nancooks for you 😂 - to be fair, her Gran is an excellent cook, especially her cakes…..

Welkbeck you are completely right. Everything is completely to suit them. They are very self focused. I am really just looking for some ideas how I can nudge it around a bit.

Yorklady well I guess I could but it just makes mess in my house. I do have some health issues which make me tired and a bit slow. What I am looking for is one or two spontaneous visits. Have my grandchildren in my home

Don't allow yourself to be taken for granted.
Seems like they view you as staff to provide a service.
So they won't drop in on you if there's no advantage to them in doing so.
I've seen this so many times.
Are you paying for the groceries too.
Just get a t shirt with a doormat logo.

Could you not collect the children from school but go to your home to cook and all eat together there ?