I have done this. Kids are now grown up. It is a great idea and it works.
I bought a decoration every year. I chose it, quickly realised that it shouldn't be babyish, but something that will last.I bought all sorts, sparkly, wooden, felt, handmade, funny, cute etc etc.
I either embroidered or wrote their initial and year on it.
They each have a shoe box full of decorations.
Kids are now 21, 19 and 16.
They love them. 2 oldest are boys, so isn't a girl/boy thing.
They unpack them every year and laugh at them and chat about them. They are pretty cool, come from all sorts of places, and some have significance. The year that dd changed her name I bought ones shaped liked initials with her new initials. Some are souvenirs from places we used to live. They got glittery cars for their 17th as they started to drive. Ds2 has a ridiculous love for dinosaurs (as an adult) and so got pink glittery dino last year which he thought was really funny.
My tree is covered in a very eclectic bunch of decorations, and theirs fit in pretty well.
Do I think they will take their shoe box off to their new homes? Probably not. But it has been a really fun thing to do, and they still do love getting those shoeboxes our of the attic every year.