I've seen posts where people have argued "oh he's just a baby" when talking about a 4 year old. But then again I've seen people say "That's not a baby that's a toddler" referring to a 1 year old.
I know as moms our babies will always be our babies...
I will always consider my son as MY baby. He is about to turn 7 and he IS NOT a baby!! I don't treat him as such either. I think that is the reason why a lot of children are behind in education and life, because their parents make them feel like babies. Children have responsibilities and they should be treated as such. He'll ALWAYS be MY BABY though!!
I always tell my kids that they'll always be my babies!
In reality however, I'd say starting when they are able to walk strong on their own, is when they are a "toddler" (after all - they're "toddling"!) :D Or, about 2 years old.