Expecting grandchildren to tidy toys.

I think instead of suggesting, you need to start telling.
Personally, I’d lay down the law prior to the next visit

Why do I allow it, is a good question! I think it’s because I fear a huge confrontation…and then not seeing the grandchildren at all….It’s crazy I know…

Yes, my sons were always taught to tidy up and we always lived as a family, with them helping with chores etc. But I think tbh my daughter in law has the upper hand here….and my son I admit, is at fault, but I think he doesn’t challenge her, to try not to rock the boat too much. Sometimes I can hardly believe that he was brought up by us! (Thankfully my other son is completely different). It was especially bad this time, and my husband is also exhausted with it all

Why do you allow it, is my question.

I think you need to do more than suggest. You should insist on them tidying up, help with the chores etc. Perhaps a quiet word with your son or daughter and say it’s all to much - you’re not fully enjoying their visits because of the amount of stress and work, say you’re getting too old to do everything and they need to pull their weight.

I'm afraid the clue is in "like their parents" - they don't know any different. Did you get your child(ren) to tidy up when they were at home|?
My grandchildren (5 & 2) are encouraged to tidy up at home and do so at our house too (with help).We make it into a game, eg put all the red cars away, can you tidy quicker than nanny etc

It’s lovely seeing the family but you are not being unreasonable about the mess and I would feel the same . If the children don’t see the parents clearing up they certainly won’t either.
I think you might speak to your adult children and tell them how you feel. Tactfully of course. Good luck.