お風呂場遊びのブームが再来。
A boom of the play in the bathroom came again to Maru.

「たくさん遊んだ後は」
After having played a lot in the bathroom

「しっかりと水分補給をして」
Maru drinks water well

「クールダウンしますよ。」
and makes cool-down in the bathtub.