A physical Man Child is a grown man, over the age of 20, who has a child's face, on the body of an adult male.
They menace that cannot be stopped. Whether this trait is a genetic or even contagious is somewhat questionable. They're everywhere and are ruining society, slowly but surely.
Tragically, they are now teaching in British schools. They usually carry around with them a friend for added security, as random attacks on Man Children are increasingly commom. Be aware: They're friends are NOT REAL PEOPLE. They are developed by the goverment to satisfy the social needs of the otherwise lonely Man Child.
"He is a Man Child. He is a menace to society! Somebody stop him before it's too late!"