This is supposed to be the parents' responsibility
A whole weekend without the parents around is any teenager's dream. You don't have to ask if your friends can come over, you can watch the movies your parents said you were too young for, stay up late, eat pizza for every every meal, and your marefriend can stay the night. All things Shining Armor had planned to take full advantage of. Except for one thing...
That thing was currently sitting at the kitchen table with a big bowl of ice cream. Twily. Now, Shining loved his kid sister very much and wasn't afraid to show it, unlike some of his peers, but sometimes she could be a real pest. Now was one of those times.
Shining's marefriend, Cadence, sat next to him, watching as the little filly ate her ice cream in silence. It was well past midnight, way later than she was allowed to stay over, but that was the least of the young couple's concerns, right now. You see, up until about twenty minutes ago, the two of them had been virgins. Usually, this would be the greatest moment of any young stallion's life, and he wanted nothing more than to bask in the glory of the newfound godhood he had achieved among his social circle. Except, his sister just had to walk in. No doubt, the pure, innocent little bookworm had seen such things that would scar her for life, but that wasn't the worst part. Twilight was an inquisitive little pony and would definitely be asking questions in the pursuit of science. A lot of questions. Probably a bunch neither Shining nor Cadence could answer. But, they would have to do their best, and pray that Twilight didn't bring it up to Mom and Dad.
Shining cleared his throat, breaking the silence. "So, Twily, I bet you have a few questions..." he began, trying his best to keep from panicking.
"Uh huh," his sister replied, not looking up from her frozen treat.
"So, uh," Shining continued, not sure where to start. "You see, Cadence and I have been dating for a little while, and we love each other very much, and when you love someone very much there's a... game you play with that pony."
"I love you very much," Twilight said. "Why haven't we played it together? Why haven't Mom and Dad played it with me?"
"Because, uh..." This was already going a direction Shining had not anticipated. A very, very bad direction.
"Because, it requires a different kind of love than what you have with your siblings or parents," Cadence interrupted.
"Exactly," Shining Armor said. "And Cadence and I have reached a point where we know we have that kind of love with each other. So, we decided we were ready to play the game with each other."
"What's the game called?" Twilight asked, cocking her head to one side.
"It's called 'sexual intercourse'," Cadence replied. Her poker face was immaculate. How was she so calm about this? "Or 'sex', for short. There are some other names for it, but they're rude to say."
"So, sex involves a colt putting his thingy in a filly's thingy?"
"Y-yes..." Shining replied, cautiously. "The, uh, correct terms you should be using are 'penis' and 'vagina'."
"But, why would anypony do that? It looked like a lot of work. And kind of gross."
"It's how babies are made," Cadence replied.
"You two are trying to make a baby!?"
"No!" Shining and Cadence shouted in unison.
"We were doing it just for fun, but it is how babies are made. We were just taking preventative measures," Cadence replied.
"Preventative measures?" Twilight asked, curious.
"Birth control," Shining replied. "Condoms, special pills, there's a bunch of ways to prevent having a baby before you're ready."
"Can two colts or two fillies play it together, or is it only for a colt and a filly? I've only ever seen foals with a mommy and a daddy, not two mommies or daddies."
"Sure, I guess..." Shining said. "They wouldn't be able to make a baby, but Mom and Dad still wouldn't be too happy if you played it with another filly, at least until you're older..."
"But, why do I have to wait until I'm older? It looks like a lot of fun!"
"It's..." Shining trailed off, not sure how to answer this.
"Complicated," Cadence picked up. "It's kind of a big decision that little foals aren't ready to make."
"Okay, but I found some magazines under Shiny's bed with pictures of a big group of ponies playing the game, together. How does that work? Do they all love each other?"
"You found what?" Cadence asked, glaring at Shining Armor.
"Cadence, I can explain," Shining replied, nervously.
"And why were there whips?" Twilight asked. "Wouldn't that hurt? Some of those ponies were crying. Why would a pony like playing a game that hurts them? Why were some of them wearing blindfolds and tied up? And why did some of the mares have boy parts?"
"Just what kind of magazines are you reading, Shining Armor?" Cadence asked.
"I'm a curious colt!" Shining said, panicking slightly. "I swear, I wouldn't dream of actually doing half of those things!"
Twilight burst out laughing. "You two should see yourselves!"
"Twilight, sexual education is no laughing matter," Cadence replied, shooting one last dirty look at her coltfriend.
"It kind of is," Twilight replied between fits of laughter. "I mean, I walked in on Mom and Dad a few months ago, and they explained everything, then. Same with the Princess, last week, and now she's planning on including some actually good lessons about sex."
"The Princess has sex?" Shining asked.
"Oh, you would not believe the number of stallions, mares, griffons, and many other creatures I've seen sneaking out of her bedroom, in the morning," Cadence replied. "She's probably done some of the things in those magazines of yours."
"I-I didn't need to know that," Shining replied, blushing.
"I do have one more question," Twilight said, changing the subject.
"All right," Shining sighed. "What is it?"
"What are you going to do to buy my silence? I'm sure Mom and Dad would love to know about all of the fun you two had together, this weekend."
"What do you want?" Shining asked, glaring at his potential black mailer. "Extra dessert? Later bedtime? A new book?"
"Well, there is a symposium on advanced magical theory, tomorrow," Twilight replied. "I do suppose I could keep quiet if you take me there and then get ice cream, afterwards."
"Fine," Shining replied. "But that means it's bedtime, now."
Without another word, Twilight gleefully hopped up the stairs to her bedroom, excited for what the next day would bring. This had been a fairly awkward night, and Shining just couldn't wait to get back to bed and fall asleep with his favorite mare by his side.
"Ahem," the favorite mare said, interrupting his train of thought. "You and I will need to have a look at those magazines your sister was talking about. From what she was saying, some of those are definitely getting burned, tonight."