I was smooching with a girlfriend in my bedroom after school one day too and my mom walked inwith an armful of clothes. She was cool about it, she just asked "Did you girls finish your homework" and put the clothes in the dresser and walked out. She never said anything about it, but when I came out in high school a few years later she just smiled and said "like I didn't already know".
Cool, huh?
I'd just tell your little sister not to worry about it, if it's your mom's problem let her stress over it.
