Comment by CTDOCodebases

So who adds more to GDP:

A. A child of any age.

OR

B. A migrant worker.

My guess is B because that person can produce goods for export while consuming local goods. Children (at least for the first few years of their life or so) do not contribute to production. They only contribute towards consumption. You could argue that they motivate the parents to produce more but increasing skilled migration in the parents industry can do the same.