If you think about it, ownership is a rather slippery concept, one based on all sorts of abstract social and economic principles. Now in one of the first studies of its kind, Ori Friedman and Karen Neary have investigated whether and how two-, three- and four-year-olds determine who owns what.
Their findings suggest that young children judge ownership based on who is first in possession of a given object. In an initial study, children aged between two and four were told a simple story about a boy and a girl playing with a toy, after which they were asked to say who owned the toy. If the story described the girl as playing with the toy first, then the children tended to say she owned the toy, and vice versa if the boy was described as playing with the toy first.