It used to be legal to send kids in the mail.
When domestic parcel post service was introduced in the United States in 1913, Americans were finally able to send packages across the country at an affordable rate.
Early on, some people chose to abuse this new service. At least two people sent their stamp-covered children through the mail before the Postmaster General was able to issue new regulations banning the practice.
The National Postal Museum still has this humorous picture on display to note those more turbulent times in USPS history.