訳:The children are not responsible.
Apologies for not knowing how to explain this in Japanese. I got this in a multiple choice thing and it said "The children are not to blame." was a valid alternate translations and this sent up some red flags to me.
This is a tricky one in English. I don't know the Japanese word, but in English, responsibility and blame are VERY different things. The idea of using "The children are not responsible." and "The children are not to blame." as being interchangeable is more than a little bit uncomfortable with me.
It becomes especially troubling or problematic if you switch this around, i.e. "The children are responsible." and "The children are to blame." These statements are very, very different, because responsibility is usually seen as a good thing and blame as a not-so-good one. Responsibility is often associated with like, doing things, taking care of things, etc. whereas blame is associated with punishment, etc.
I recommend non-native English speakers to be very cautious about the use of the word "blame" because it has such a strong negative connotation and can be associated with group conflict, punishment, condemnation, etc.. I'm especially cautious about using the word around children.
I understand the meanings of "The children are responsible" and "The children are to blame" are completely different in English, as you pointed out. However, "責任がある" in Japanese means both, depending on the context/situation.