Among the things that the Sahaabah (radhiyallahu ‘anhum) enquired from Nabi (sallallahu alaihi wa sallam) was a woman’s relationship with her brother-in-law. Nabi (sallallahu alaihi wa sallam) replied that he (the brother-in-law) is death.
We tend to restrict purdah to outside the home, but in the home we leave out these aspects. There is free mixing between cousins, brothers-in-law and sisters-in-law etc. We do not understand the harms and consequences that arise from this.
The children need to be educated regarding the laws of purdah. If nobody speaks about these aspects now, then the consequences are serious. If it’s not in school then it will be through the media and internet that they will become enticed with all sorts of related evils.