expression, noun
Refers to the difficult period around age two when toddlers often become defiant and throw tantrums. A set phrase used in parenting contexts.
魔の２歳の娘に手を焼いている。
I'm having a hard time with my daughter who is in her terrible twos.
魔の２歳はいつか終わると言い聞かせている。
I keep telling myself that the terrible twos will end someday.
イヤイヤ期 is a more general term for the 'no-no phase' in toddlers, while 魔の２歳 specifically refers to the age of two.
Calque from English 'terrible twos', combining 魔 (demon, evil spirit) with ２歳 (two years old).