Formal:
* Le petit fauteur de troubles: This is the most literal translation and is appropriate for formal situations.
* Le petit perturbateur: This is a more general term for someone who causes trouble.
Informal:
* Le petit voyou: This is a more colloquial term for a troublemaker, often used for children.
* Le petit briseur de règles: This literally means "the little rule-breaker" and implies a mischievous child who enjoys bending the rules.
* Le petit dégourdi: This means "the little clever one" and suggests a child who is mischievous but also resourceful.
* Le petit farceur: This means "the little prankster" and is a good choice if the troublemaker is known for playing tricks.
The best choice will depend on the specific situation and the tone you want to convey.