I think sometimes our adult children completely forget that there are other aspects to our lives besides being an always available parent to cope with whatever needs they may have. I think they also forget how old we are – and, of course, however fit and well, we are old compared with them.
That said, I do think your son's attitude and his, frankly, contemptuous treatment of you are disgraceful. I think they would still be disgraceful if he were paying you childminder rates for the hours of care you give your grandchildren. That you are doing this because you love him and your grandchildren seems to have escaped his notice. There is no rule that says the parents of adult of children must ignore their own needs and wants in later life and be at the beck and call of those adult children – but that seems to be his view of you.
I do a lot of childcare – my daughter has six children ranging in age from one year to 14. She is also about to take her final exams (next week) for her psychology degree and the baby has been unwell so I have been putting in more hours and days than usual. Like most of us on Gransnet, I love my daughter and all her family and help very willingly, but I wouldn't mind betting that after next week a huge bunch of flowers and a bottle of wine will be coming my way. Not, of course, payment, but a token of genuine gratitude for the favours I have done.
Perhaps your son needs to recognise that willingly offered favours require some kind of thank you, even just a verbal one. I don't think absentdaughter ever collects her children from my house without a "Thank you Mum" and a kiss, however harassed or pushed for time.