Since our parents took care of us, now it's our turn to take care of them.
Literal
Parents [subject-が] us [possessive-の] care [object-を] did [reason-から], from-now us [subject-が] parents [possessive-の] care [object-を] see turn is.
面倒を見る (to look after) appears twice — once for what the parents did, once for what the children will do. 番だ (it's one's turn) marks the current obligation. から (because/since) gives the reason. 僕ら uses the male first-person plural.