DH and I were talking about this today - if you have two children of the same sex, will you expect that they share one of an item they both like? So say you have two boys that love super heroes and Christmas rolls around - do you buy them each a Hulk or whatever or buy one? I grew up with a brother so this didn't come up but DH has two brothers and they were each given their own "x" at Christmas.
We have a playroom that, through the generosity of family and some generous hand me downs is stocked to the freaking ceiling so I was already thinking about what the heck I would ever buy DS2 unless he develops a love for something his big brother doesn't love. Right now it's filled with general toddler stuff plus the Cars and superhero stuff Aiden has fallen in love with.