Why they do this?

someone could create an email for their newborn and send it pictures and videos of him growing up and loving and laughing with his family, then once they're old enough they give them the email and password!

I've heard of parents who create emails for their children at birth, so that school forms and things can be sent to that email so it's easier to separate them. But I've never met anyone who actually does this.

Probably just a convenience thing.

My dad made an email account for me when I was little (though I might've been older than 1 year, I think I was like 5 or 6) so that nobody could take that username/address. I actually still use it but not very often.

Could be for companies that just started