Interesting question ^^
I don't want kids, but I would be happy if my hypothetical kids had the same interest about toys.
But sharing the same interest is not sharing the same toys ^^
So even for a same toy line collected, I wants that my kid have his own toys.
As I mostly collect vintage toys, it's difficult to imagine my delicate precious toys in child hands >__<)°
But with his own toys, I will be very happy to teach him passion for collecting and respect for the items collected (no, it's not a good thing to crush toys with a hammer !!).