It's quite colloquial to say "I think we all ought to cut them some slack".Well, yes, it does mean 'a bit more slack' but if these were British parents talking in an everyday situation, I think they might say: "I don't think we should be too strict with each other". I find it difficult to translate the sentence more literally in a way that British parents would probably say in that situation.
You may well be rightIt's quite colloquial to say "I think we all ought to cut them some slack".