Possible Clues:

• Shenanigan pullers
• Wee pranksters
• Some troublemakers
• Hell-raisers
• Baby-sitters' banes
• By the end of the letter I am making them mischievous
• Rambunctious kids
• Devilish folklore creatures
• I am coming at last in a mischievous manner
• Pains in the you-know-what