We bought Charlie a jigsaw puzzle over Amazon and when I gave it to him, he asked me who bought it for him. I said, "mommy and daddy bought it for you," and he seemed satisfied.
Then this weekend, I bought him two books, and he saw me pay for it at the cashier. Later when I started to read it to him that night, he asked me, "Who bought this?" I wanted to tell him, "OMG you just saw me buy this!" But I just said, "Daddy bought this for you, remember we were at the bookstore today?" He said he remembered, but I actually don't think he cared about the details. He just always likes to ask who bought something... it's like his first default thought when he sees something.
This is the typical conversation: he will ask who bought something, I will tell him, and then if it's not me I will usually suggest that he thank that person... and he will say something like, "Thank you, mommy!" (We also do this when he asks who made him his dinner.) So I try and hijack the whole process and turn it into a gratitude thing. Not sure if that's useful/helpful, but it gives me a sense of control haha!
It's become such a common question lately though, that I wondered if other kids are also fascinated with this? Do your kids ask where things came from?