The Mingo Kids first appear in Hard Luck, where Greg happens to step too close to their territory. One of the Mingo Kids intervenes and warns Greg with the threat of Meckley harming him. Greg then takes the long way to school, fearing the Meckley might attack him. While shopping for shoes, he imagines getting a pair of shoes with wheels to outrun the Mingo Kids. Greg chooses to join an after school activity to wait out the Mingo Kids before leaving school, which leads him to join the Yearbook Club. Near the end of the book, Greg and Rowley are chased by Meckley and another member of the Mingo Kids.
The Mingo Kids later appear in The Meltdown, where Greg and Rowley stumble into the inner sanctum of the Mingo clan. Greg accidentally takes Meckley's belt buckle. The Mingos find out and sound an alarm, while Greg and Rowley escape. The Mingos eventually join the snowball fight against the Lower Surrey Street and Upper Surrey Street kids.
The Mingo Kids appear to be an organized group led by Meckley, their tough leader. They appear to be very territorial, as they chase anyone who sets foot in their woods, and warns them if they are near their terrain. They also might be war-like, considering they join the big snowball fight in The Meltdown. They are also shown to "hibernate," according to Greg.