When I'm a baby

My 3-year-old sometimes talks as if she will turn back into a baby at some point. If she is talking about her younger sister,m she may say, "When ____ is bigger, she will sit in my carseat, and I will sit in her baby seat."
Or she will say, "When I'm a baby, I'll use the baby באדי (bath)."
"Oh, when will that be?" I ask.
"After I turn 4 or 5."