If young girls go alongside with older sisters, the olders siters can lead them and create atmosphere of modesty. And at home borhter, father can remind and speak to young sisters if they fail in behavoir. Why you are so unwilling to admit this kind of communication is better that forbid sister to go to masjid. I am also for - not going to mosque regularly, anyway I think communication is more important - for example by saying to sister that she could preferrably pray at home. No body is saying this to them and help them to find comfort within quran and hadith? May be we muslism do not communicate enough... what do you think? w salam