L. (3 years and a half) has become very defensive of his territory, especially in his dealings with his older sister. He started by demanding her not to touch him or the toys he was using. Later he began to enforce a kind of “exclusion zone”: he doesn’t want his sister to get too close to him, especially when he’s playing by himself (with his toy cars, etc.). Of course, this doesn’t happen all the time; they often play together and get along well. But sometimes he does get very territorial and shouts or cries asking her to leave (in his jargon: “¡ite!”), and if she doesn’t obey he tries to recruit parental help.
Lately, in what I see as an increase in this kind of territoriality, he seems to be concerned about “intellectual property”: whenever he says something and is echoed by his older sister (or other people) saying something identical or very similar to what he just said, he tells her not to copy him (“¡No me copies!”). He’s enforcing intangible boundaries that protect his identity; he’s drawing an assertive circle around him and he’s self-confident enough to try to deter his older sister from crossing this limit.