expression, noun
Refers to the difficult period around age two when toddlers often become defiant and throw tantrums. Used as a set phrase.
うちの子は今、魔の２歳児で、毎日大変です。
My child is in the terrible twos right now, and every day is a struggle.
魔の２歳児の時期はいつか終わると言われています。
They say the terrible twos phase will end someday.
イヤイヤ期 is a more general term for the 'no-no phase' of toddler defiance, while 魔の２歳児 specifically refers to the terrible twos around age two.
A direct translation of the English phrase 'terrible twos', combining 魔 (demon, evil spirit) with ２歳児 (two-year-old child).