When collecting passports from US Travel Docs (or Team Stanley), you will need an authorization letter if collecting passports for someone else. Even if you did a family application and a husband goes to collect passport for his wife and/or child – an authorization letter will be need for them.
Here is a sample authorization letter. Best is to fill up one letter per applicant. In case of a minor, the parent can sign on the child’s behalf but you’ll also need a copy of parent’s passport.