"It's natural for Exton to want to bite her once in a while and it can start off as a little pet and then it turns into a nibble... I think it's just establishing dominance, but she'll be running stuff at some point." Actor ROBERT DOWNEY, JR.'s three-year-old son Exton is still adjusting to life with his newborn sister Avri, who was born in November (14). The Avengers star shared the first photo of his five-month-old girl, with his producer wife Susan, on The Late Show with David Letterman on Thursday (23Apr15).