It's really all relevant to the circumstances though. I bought my DGS 8 presents averaging £25 a present and also gave my daughter money before Xmas towards the presents she bought him. But she is a single parent, only working part time and I have been lucky enough to have had quite a lot of work this year on top of my pension. My sister couldn't even be bothered to pop a fiver into a card for her only grand nephew, and my ex husband gave him money. His father doesn't celebrate Xmas, he didn't even send a Birthday card let alone a present, and the GPs on that side are in Afghanistan, my GS has never met them. The only other Xmas present he got was from my present partner's daughter. Not every child has a large extended family.
I knew most of the presents would be cast aside in order to get to the one he specifically asked for - 2 Lego Dimension packs, but that the others would be returned to after Xmas. Those ones will stay in my house for when he is with me and a week on, he has already gone back to them and yesterday we had a great afternoon putting together 2 Lego Ninjago sets. I think of Xmas presents as an investment for ways to occupy him over the next year.
I feel the OP has had a tough time on here, she bought with love for her DGCs. I think I would have put all the presents into a large box for each child to make one present each for opening, but I feel for her. I think it is probably more difficult buying for children of a DS and DIL, than a DD, everything I buy is discussed with my DD first.