mosher, I completely agree with your post. Since I don't read the comics, Carl's age is irrelevant to me. I'm especially in tune with your second paragraph.
I seem to be internally (as a mother of three) hung up with Judith learning to walk, and the idea of trying to keep a toddler on a leash. That little girl is going to need walls and a floor. Her legs will atrophy if she's constantly carried. And once she can walk, that's when the crying would start with her annoyance at being confined in someone's arms. The birth of Judith has saddled the writers with quite the problem. We need enough of a time jump to get her on her feet and able to run.
Even if she is walking and running, she isn't going to be very fast. She will slow the party down when they are trekking and someone will have to hoist her up when they are being pursued. Still, I really hope she makes it and we get to see Lil Ass Kicker the Avenger.