I completely 2nd everything pp said. Dcfs often expect another child while in our care and we do get into a bind with our numbers. We can only have so many children according to each state. I am facing that problem in the next few months and am hoping like crazy that it works itself out. I don't want to have to do to my dcfs what's happening to you. I love all my dcfs and picking one to let go of temporarily would be extremely difficult and probably cause me to lose the sibling.
Guess what I'm trying to say is please see both sides because in an issue such as this one, there are definitely 2 sides to consider. Is it common? I'm not sure but it does happen and probably mostly to private daycare homes where we can't really afford to hire an assistant; we end up having to pick and choose.
This is a business first so we do need to consider making a living. As for myself, I try to consider all angles and make it work for the majority, without compromising too much.
As it turns out one of my dcms had a baby in December but I cannot take her until summer, when my under-2 yo twins will be staying home with teacher dad. Then I just found out 1 of my other dcms may very well be pregnant and is due around Sept. Then a former dcm whose dd entered K, stills want to bring her baby this next fall. I definitely have to say no to somebody.
Good luck with your choice and search for child care!!