I don't think overpopulation is a problem worldwide. If anything the problem is inequitable distribution of resources and policies that give no thought for future problems, because all politicians want is to be re-elected(or keep power by force). So the problem isn't that there aren't enough resources to sustain everyone, the problem is there aren't enough people who help. Also politicians are corrupt and incompetent.
You're right about adoption though, 75% of my siblings are adopted, and there are always children who need good homes.