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.
But what if the children were simply attributing ownership to whichever person was first associated with the toy, rather than in possession of it? A further experiment involved telling the children that the girl likes the toy, and then that the boy likes the toy. However, in this case, the children were no more likely to say the girl owned the toy than the boy did, even though the girl had been associated with the toy first (the same was true with the sexes reversed).
Finally, Friedman and Neary wanted to see how easily the first possession rule could be overcome in the context of gift giving. When the young children were told that the boy has a ball which he then gives to the girl as a present, they still tended to say that the boy owns the ball (the reverse being true if the story began with the girl in possession). However, when the gift giving was made more explicit (a wrapped present on the girl's birthday), then the first possession rule was broken, and the young children correctly realised that the girl now owned the gift.
The researchers said the most important next step was to find out where young children get this rule about first possession from. They surmised that it could be learned from hearing utterances like ‘‘It’s her doll, she had it first’’, or it could be innate, the product of a "cognitive system dedicated to reasoning about ownership."
FRIEDMAN, O., NEARY, K. (2008). Determining who owns what: Do children infer ownership from first possession?. Cognition, 107(3), 829-849. DOI: 10.1016/j.cognition.2007.12.002