Oh come on girls. Moms know everything. Its just one of those things that is instilled in them when they give birth for the first time. Then it depends on how openly you talk with them. Some may keep it private and some may confront you. But Im sure most that do confront do it because they care.
My mom found my stash of cloths when I was a teenager and it was years later while I was married and it came out to my wife that mom ever said anything about it. That has been 20 yrs ago, the subject never came up again and to this day I still wonder if she knows I still do. To afraid to talk to her about it. Shame on me.