Is there a way to adopt a child already in game?

Thanks everyone. What I did was I went ahead and moved him in (the adult "dad" who was going to adopt them....he had started falling in love with their mother in a crossover / collab video we did), did the adopt as caregiver thing, and used MCCC to add the relationship as father and daughter (the baby I will have to wait until he ages up).

@izbthnndgls, I wish I would have thought of creating a "social worker", that's a really good idea! Thank you everyone for all of your help!