If I was to have a nanny, I wouldn't let the sex of applicants become a determining factor. If my husband and I took a liking to them and they were qualified - and if their references checked out, I imagine we'd hire them.
If I was going to have a nanny I suppose I would have a male nanny if he was qualified and the kids liked him. It would depend on references and stuff. But I'd rather not leave my kids with someone else all the time like that anyway.
I think it would come down to whether I felt a connection with them, whether the kids connected with them, whether they are qualified, references etc. I recently advertised for a "helper" around the house (nanny / housekeeping) and while I would have been surprised if a male had responded to the add I would still have interviewed them and checked references etc