[masaegu]

Here are the lyrics and a little explanation.

「息子さんは中３で受験勉強してた
夜食のカップヌードル、お母さんが忘れた
息子さんは拗（す）ねた」
＿＿＿＿

中３　＝　中学３年生
That's the last year in junior high, so you study for the high school entrance exams. This study (more like cramming) is called 受験勉強（じゅけんべんきょう）.

夜食（やしょく） = late night snack. 　It's different from 夕食 = dinner.

拗（す）ねる = to get sulky