We buy a personalised bauble for each child each year that has their name and the year on it. The idea is that when they are 18 and leave home, they have their own collection for their tree. My eldest is 8 and therefore has 8 in his box and it is his favourite part of christmas - getting them out and hanging them on the tree. I have 3 kids, so they each have their own box and decorations and they hang them on the tree themselves. It makes for a lovely meaningful tree too.
We have started buying them for my nephew too in the hope his parents will continue the tradition for him.
I first heard the idea on mumsnet many many years ago so I thought I would pass it on.