Once you’ve acquired the Paris castle in the game, you can adopt a child.

You will be taken to the ground floor of the castle, where an action pin will be visible above the baby bouncer.

There will be a phone icon there; tap it to bring up a popup that asks, “Call for adoption? ” The “Call” button initiates a phone call where you can choose to have a baby of the gender of your choice. 

You have to wait 24 hours for the baby to arrive after the call is over.