The same place they get them from in real life I suppose.

Props dept, I think?

There are storks. They find these little people in a special cabbage patch. From there, they fly them in.
You asked a pretty question; I've given you the ugly answer.
Fasten Your Seatbelts….
It's Going To Be A Bumpy Night!

They’re bred and raised on an island in the Caribbean owned by Rupert Murdoch. This is also where he raises the sexy blonde Fox News anchors
Stop.

Who played the baby in "Rosemary's Baby"?
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I GameBoy

A casting agency places an ad and many willing parents show up ready to get their kids picked for a part in a movie or show.
Works the same for extras…I was one before…so I know how that goes.
Are you okay?

Sometimes the baby is the director or producer's newborn kid. For example, Sofia Coppola is the baby being christened in The Godfather, which was directed by her dad Francis Ford Coppola.
You've seen Guy Standeven in something because the man was in everything.

I guess parents bring their kids to auditions for parts. They usually use twins
If we take the time to see with the heart and not with the mind, we shall see that we are surrounded completely by angels ~ Carlos Santana

Hmm…good question.