Right now, our youngest is a too little to really understand (he's 19 months), but we still tried to spend the same amount of money and give the same amount of gifts. DD is 4 though & we obviously spent a little bit on her this year, but I don't think DS is going to care very much. As they get older, we'll care more about making it 'even'. They're both going to end up playing with each other's toys anyways, haha.
I usually do equal amount in cost. Not quantities LOL this year I did neither. LOL
I spend more on my oldest but she has less. I got more for my youngest but it cost less. And I'm not done for my middle. I just returned a wack load of stuff I got her cause my parents bought the same. LOL so now she only has 1 gift plus her basket. LOL so I'm shopping for her tomorrow lol
I suppose it depends on age and interests. If you have say two 12 year olds and one is into sports and just wants a ball and a new pair of shoes its not going to be as expensive as the one who wants a new x-box