Generally, I don't understand why anyone would put a "full" name if they only intend to use the short form. If you want to call your kid "Ben" just call him Ben! He doesn't need to be "Benjamin" on his passport!
I would hesitate with Peggy though. Maybe it's just because I'm not fond of it, but it sounds more nickname than name to me. Like calling your kid Flossie or something.
That's just my two cents!