You should always fulfill your responsibility to protect your kids from harmful things, and nothing more harmful and damaging than sinful acts. If your husband allows your kids sinful acts, that does mean that you have no responsibility to protect them. You must talk to him in a suitable way to prove to him that both of you are responsible to protect your kids. You also need to explain to your kids the as much they can understand the concept of good and bad. Your husband will not permit your kids to eat a sweet which contaminated with microbes because it is harmful for their health, so, how can he permit sinful acts which are more harmful?
Do whatever you can (with wisdom) to protect yourself and your family from Hellfire, as Allah said: O you who believe! Ward off yourselves and your families from a Fire whose fuel is men and stones. Sura 66, Verse 6.