There is an amusing photo from Flickr here:
QUOTE
Description: This city letter carrier posed for a humorous photograph 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.
I love the expression on the mail carriers face; I'm thinking the kid must've needed changing!
This is part of a collection from the Smithsonian Institution!