I have no idea when kids generally do this. I think we confuse ours a bit because we call her different things-- Fiona, Fia (my family), Nona (her dad), Boo/boobaloo(me. I dunno why). Sometimes I think she knows her name, or at least seems to respond to Fiona and Boobaloo. But then other times I think she's just responding to me talking to her and I could call her anything and she'd look at me lol.