I hear a lot of parents (and other non-parental adults) lamenting that their children seem to have no idea where their food actually comes from. Mostly the answer to the question "where do we get milk from?" is not "a cow" but "the shop".
Last weekend we went to Staglands with Aunty L, Uncle B and their kids. Being spring, the place was alive with chicks, ducklings, goslings, kids and lambs.
When Isaac got to this pen, and we told him that this was a lamb, this was his reaction:
I guess he must know at least that much, then.