THE DIFFERENCE BETWEEN XXIII

What's the difference between:

1. A delivery boy and a delinquent boy?
2. A child's plaything and a yes-man?
3. A formal dance and a traditional folk song?
4. A kindergarten activity and a private investigator's job?

Answers:

1. Errand and errant 
2. Toy and toady
3. Ball and ballad
4. Show and tell and Shadow and tell