I do the same thing with my ex...it's funny you should post this. He does it to me too. The story is we are both raising grandchildren and live 130 miles apart and we don't get to see the others grandkids very often.
The two he has are 10 and 12. The ones I have are 7 and just turned 4. It is hard for me to know what they are wanting or needing, such as games for electronics, if I don't know what they wear or use. Same with him buying for these kiddos.
This year I gave him a list of some things we just cannot afford, they make 3-4 times the money we do and usually buy very nice useful gifts. I have no issues with previous gifts at all.
On our list was several movies, toys, games, etc...and a few clothing needs such as Soccer shoes, which Granddad is a big soccer fan (coaches both boys and plays) and knows the best ones to get.
He took the list and still bought what he wanted along with a few things on the list. He got a couple of the movies and a sit and spin for the little guy and then he bought a new bike for the girl and some other things on the list too. His wife is wonderful and she has lots of years in child care and knows just how to pick age appropriate stuff and what will really hold their attention.
I got a list from him too and he is getting both the boys new game systems so we are getting them some stuff from Game Stop.
As for the grandkids dads they usually just send cards with money/gift cards in them and we let the kids spend a portion of them on anything they want and then we buy anything they really need with the rest. Both dads pay regular child support too so the Christmas money is extra.
My daughter is still in rehab and even when she wasn't she never bought them anything or paid child support so I don't expect anything from her and we put something under the tree from her.
So, to sum it up, I like getting a wish list. It makes shopping very easy.