Arthur was now old enough to change Kate's diaper, much to his dismay. He had never changed one before and now his father was making him, it was so gross. He hesitated before opening it; at least it was only number one, and not too much of it. When he opened it all the way it was the first time he saw what girls look like, as sad as that was. As he cleaned her up he became curious about it and began to touch it even though he didn't need to anymore. He let a fingertip slid along his baby sister's mound, feeling every curve of it, and the slight wetness. He wondered why there was an opening and decided to explore that as well by slowly sliding his finger into it. It was even wetter inside and he moved his finger around, trying to reach every place he could. Kate squirmed beneath him, he could tell he wasn't hurting her but she did seem a bit uncomfortable. He didn't know why he was doing this, he just wanted to know about it, he didn't even know if it was ok or not.
Just then his father, their father, walked into the room and gasped, "Arthur, what are you doing? That's your sister, it's wrong to do that. Not to mention she's just a baby." He moved to the changing table and lightly slapped Arthur's hand away, "You're not supposed to do stuff like that until you're older. And you're not supposed to do it with family members."
Arthur fidgeted nervously, worried he was in trouble, "I-I'm sorry dad... I just wanted to know what it was."
David put a new diaper on Kate before turning to Arthur, "How would you like it if someone touched your lower parts without asking?"
Arthur frowned and looked downward, "I don't know... It feels good when I touch myself... maybe that would feel good too..." He looked over at Kate, "Do you think it felt good for her?"
David had been trying to keep as calm about this as possible, which wasn't easy, and that question didn't help, "Um... well, she's too young for it to feel good; it probably just made her feel weird." As he said that he tried not to think about Arthur touching himself, which was actually starting to get him hot.
"Oh..." Arthur muttered, then he hesitated before saying in a shaking voice, "I feel like touching myself now..."
David flushed, now he was really hot and bothered. He shifted uncomfortably where he stood and answered in his own shaking voice, "If you feel like it then do it, son, it's a natural thing that everyone does."
Arthur wrung his hands and looked up at his father bashfully, "Does that mean you touch yourself?"
David swallowed and nodded, "Y-yes... Like I said, everyone does."
The young boy didn't know why his father seemed so nervous but he was too, "I kind of... want you to touch me," he said, blushing.
The man's eyes widened and he felt stunned, "W-well son... Family members can't do that."
"Why not?" he asked timidly. "I... want you to make me feel good." He could feel there wasn't something right about all this but he couldn't help wanting his father to do this.
David sighed and put Kate into her bed before taking Arthur's hand and leading him back to the boy's bedroom. He shut the door behind them and hesitated again, "Arthur... if I do this for you no one can know, especially your mother."
The young boy nodded sheepishly before reaching down to touch himself, "Please dad."
David's stomach tightened at the light plea, he knew this was so wrong but he was getting beyond turned on. He moved toward his son until he was right in front of him and reached out to touch him as well, his breathing shallow. He could feel his son's member slightly hardened underneath his touch and it made cock twitch. He bent down and put a little bit more pressure into his touch and a precious noise left his son. "Does that feel good?" he asked in a whisper.
Arthur whimpered and nodded, unable to really say anything, it was a lot better than when he touched himself. He removed his hand and let his father take over completely. His body began to move in ways that he didn't mean for it to, and more sounds left him. "Dad... dad..." his hands went to his father's arms and he shuddered, "it feels really good..."
David was shaking now, he was pleasuring his son and it felt odd, he felt guilty, but he was also very aroused, "Have... have you ever touched yourself for this long?"
The boy shook his head, "No... I never felt like this when I did it."
David moaned as he continued to touch him, his own member getting extremely stiff. Eventually he couldn't take it anymore, he needed release, and he picked Arthur up and carried him to the bed. Sitting down David set his son on his lap and groaned, the pressure feeling amazing, Arthur let out another whimper as well. David held onto Arthur's waist and let his hips roll up into the small figure on top of him; he could feel their cocks brushing together through both their pants. He had already been so close that he knew he didn't have to do this for very long, and he could tell his son was close too. Both of them where panting and moving, and Arthur couldn't keep from touching himself again. They did this until both of them reached their peak, both hardly able to breathe or control themselves. Then, in a moment, they both released, and David held his son tightly as Arthur clutched onto him.
After they had ridden out their orgasms David continued to hug his little boy, not sure how to cope with it, even though his son seemed fine, "Arthur... I really shouldn't have done that, and I'm sorry."
Arthur nuzzled into his father, "No... don't be sorry, it felt so good dad. Thank you."