Here is another article by Mr. Wait in regards to adoption of children. As always, it is eloquent and thorough. I've often wondered about adoption being compulsory since the thought of adopting children overwhelmed me in an already fruitful marriage. So, I particularly like this excerpt as a clarification on the subject:
...the concept of adoption is a Biblical idea but it is only explicitly
found in the New Testament. But the only sense that Scripture speaks explicitly
of adoption is the spiritual adoption of believers as the children of God. From
the doctrine of adoption we see that it is by free choice rather than
compulsion. So, perhaps we can say that we are free to adopt children who
otherwise would be outside of the covenant, but we are not required to do
so.