、！
If you get pee on the toilet seat, wipe it up properly!
Literal
Toilet-seat [on-に] pee did-[if-ちゃったら], properly wipe [imperative-のよ]!
しちゃったら is the casual contracted conditional of してしまったら ('if you end up doing'). 拭く (ふく, 'to wipe') is the key verb. のよ is the feminine imperative sentence-ending: の (explanatory) + よ (emphatic) — a mother's scolding tone. The domestic content with baby/child vocabulary (おしっこ) and maternal speech patterns makes this very slice-of-life.