Rather than hound your children in December to ask for them to buy your grandchildren's toys or send them direct links to things for you "That way you know it's something they'll really like".
How about next year make more of an effort to be involved? Talk to your grandkids, take them on days out, take them to Smiths Toys or whatever and find out yourself?
I've got homework, Christmas Assemblies, Christmas parties, Christmas dinner to prep and cook, work, kids to clean, feed and clothe.
I have to plan presents for my own kids, presents for you, presents for other grandparents, presents for teachers.
Finding out your grandchild likes Peppa Pig or Fortnite is not exactly an interrogation skill and I'm sure you can get by with not doubling up too many presents.
I'd rather have to return or donate one or two toys than do all your Christmas shopping as well as my own.
If you're not sure you could try something like, I know X loves Sylvanian Families - does she have this pony set?
It feels like a lot on this year.