Does it make sense to get an au pair?

Every week a Guardian Money reader submits a question, and it's up to you to help him or her out – a selection of the best answers will appear in Saturday's paper. This week's question My wife's gone back to work now our children have started school. We've really struggled with childcare and are considering a live-in au pair. Does it make sense financially? How about socially? Some friends have been really sniffy when we mentioned it, suggesting we've sold out. Have we? What are your thoughts?