You watch your girlfriend in the little boy's appearance masturbates like a little pervert for the first time, you can see how she's starting to enjoy it. “oh man, honey, are you going to stay there or join me?” S/he asked reaching towards your belt buckle.
“Well I don’t know yet,” you reply unbuckling your pants and taking off your shirt, “should I show you how or join you in a skin-suit?”
“Show me how first, I’m only a little kid after all.”
Both of you are now nude, a hairy 16 year old and a pubescent clean-shaven 10 year old. You offer your hand to exit to the living room instead of basement, but instead s/he grabs your flaccid penis as a guide as you both head back out of the basement. “So now what, I don’t know about anal stimulation babe, but otherwise let’s make me cum!” s/he exclaims jumping up and down, her penis bouncing alongside, “damn, this thing jiggles like boobs, but not painful.”
You stand there bemused at your girlfriend’s excitement, so you lead her over to your sisters room, open her underwear drawer and pull some out, “What are you doing? You know I’ve seen more than… oh…”
You smile as you see your girlfriends erection at women’s laundry, so you take the panties in a fist and start stroking it surrounding her/his penis, “keep the stimulus up, I’ll find some with her musk if you need, then I’ll join you in perverting my sister’s clothes.”
s/he nods looking spaced out almost drooling with the stimulant you’ve provided, “Oh honey, I think… I lo… I love… I love this!” S/he moans in spasm as her/his sperm coats a pair of your sisters panties. “Oh, my dear girlfriend is a perv for my sister so much so I couldn’t even join, well that’s dissapointing…”
S/he now looking tired stares apologetically, then goes and nuzzles up near your penis and kisses it, “Sorry honey, I just couldn’t help it, I get it now at least, forgive me?”
“Yea, let’s take a nap here and we’ll have dinner and go again after, then I’ll join you in wearing a skin-suit myself.” You reply then bringing her into your sisters bed, spooning your girlfriend and fall asleep, not before putting the cum stained panties on him/her.