My two boys have a three-year gap. DS2 is 15 months. So far, I haven't bothered much with fairness in general, and particularly not for Xmas. DS2 has loads of toys, he has all of DS1's old ones, and plays with many of his current toys, too. So I don't really bother buying him much new stuff.
I know he won't notice this year, but will he when he's 2? Or 3?