What skills would be used for construction, building, architecture?

More specifically, what would be used for making toys.

I wouldn't be against someone using ranks in craft weapon/armour to represent another craft. Craft Trap (Engineering) could also be applicable for little mechanical toys.

And would it be possible to craft toys IG, if you have the right supplies, or maybe repair/change ones already existing?

It's possible, yes. Though the DM team cannot be expected to be on-hand for it at all times.