From the archives of the National Postal Museum comes this photo of a postal carrier with a young boy in his mailbag.
After parcel post service was introduced in 1913, at least two children were sent by the service. With stamps attached to their clothing, the children rode with railway and city carriers to their destination. The Postmaster General quickly issued a regulation forbidding the sending of children in the mail after hearing of those examples.
Link, via Good Mail.