いたずら盛ざかり

noun

mischievous age; age when children are full of mischief

Refers to a stage in childhood when kids are especially playful and prone to pranks; often used with a nostalgic or affectionate tone.

• うちの子こは今いま、いたずら盛ざかりで、毎まい日にち何なにかやらかしてます。