I'm an uncle!

I got the news last night that my sister in law gave birth to a baby boy. I wonder why people always specify that it was a "baby" boy. Is that really a necessary adjective? Are there a lot of people who give birth to full grown boys, such that you'd have to specify to avoid confusion?"Really? you had a boy? a baby one or full grown? ateenager? that must've been painful!"I don't know if it was a "