I had the misfortune to watch the movie Baby Geniuses last night. Then I read some reviews of the movie. I know- should have done it the other way round. I was surprised that the movie and reviewers called the kids babies. The kids in the movie were between 18 months and 2 years old. I would define a baby as a human less than one year old. Am I wrong?
I understand the movie studio wanting to call the kids babies- they think it may help sales. But why would a reviewer call a 2 year kid a baby?
Up to one year old is one definition. Here’s a study that uses the term “babies” for those up to two years old (“…babies during the age of one to twoyears.”). In some rural areas, “babies” is used colloquially for young children up to several years old. So while in one sense you’re right, you’re wrong to think the term can only apply to those age one year or less.
There’s no official definition, as far as I am aware, which maybe makes this more of an IMHO-type question. One might say that, as long as their age is still being described in months rather than years, they could be considered babies.
Since most kids learn to walk around age one that seems to be the transition point of baby to toddler.
I think the definition of “baby” is different for people without kids, who don’t care to be that exact. For instance, I don’t have kids, and to me a “Baby” is any small child 
that hasn’t learned to talk and make sense yet. I don’t mean make complete sentences but talk so anyone can understand. I don’t mean the kind of babble that babies make that only the mother or dad can understand.
I think that once the wee little one can talk and form complete sentences and be understood by anyone he’s graduated.
In Jewish tradition, the fetus is not considered viable until after it graduates from medical school.
That’s not completely true. A successful pass of the bar exam (one step up from the bar mitzvah) or various finance licenses also make a nice Jewish baby viable much to the relief to the mother.
Certificates of gemological study will suffice, too.
When my daughter started school at age 3 (significant speech delay) her teacher informed us we needed to convince her she wasn’t a baby any more and that she was a big girl. My husband looked at me, I looked at him, and we looked at the teacher and said “Boy, are you talking to the wrong folks, she’s always going to be a baby and you can’t make her grow up!”
We are late parents, she’s still our baby. A little large and verbose, but I look at her, and yeah, she’s just a baby. 
What? She can start dating when she’s 60! (And we are both dead)