Sometimes people ask this question instead of asking number one. I understand what people mean when they ask it but I would recommend considering a few things before posing this question to a family who is pursuing foster care or adoption.
One, many people come to adoption through a struggle with infertility. Asking this question could draw up some serious emotions of pain and loss. Frankly, emotions that they may not want to discuss with you in the grocery store or church lobby.
Secondly, people who want to adopt consider the kids they are adopting THEIR OWN. I know, I know…it seems like it is semantics but it is really important. I mean, if the kids do not belong to them, who do they belong to? When you ask a question this way you are invalidating the legitimacy of this family. Good foster and adoptive parents will love and attach to a child just as if it was a biological child. Those kids are theirs for however long God entrusts them in their care whether it is three days or eighteen years.
Okay, but your still curious. What is a better way to ask this question? I like how T & W put it: Do you think you will continue to grow your family? You still may not get the exact answer you want. But your question will be polite and not offensive to the family.