Whoever said this can not possibly have children. Small babies couldn't care less about toys which move in and out of their hands, except perhaps for the serious matter of tasting them.

They soon learn to say the word that other people use when they want to keep stuff. The actual meaning of the word, and that some people's ownership seems to have legitimacy, doesn't dawn on them until later.

(Just to clarify in the age of the Internet: I think we should respect ownership. But the argument that we should do it because it's an innate concept with babies is a bad one, even if it was true.)