One popular storyline could be Piper dealing with the challenges of her pregnancy while still protecting the world from evil. She might have to balance her new physical limitations with her duties as a Charmed One. Another could be how her sisters react and support her during this time. Maybe they use their powers in unique ways to help Piper through the pregnancy.
Definitely her sisters, Phoebe and Paige. They are her closest family and would be there for her throughout the pregnancy. Leo, as her husband, is also crucial. He can provide support and love. Then there could be some of the recurring good witches or magical beings who could offer their help or advice. For example, Grams could appear in Piper's dreams to give her some grandmotherly wisdom about motherhood.
For Naruto and Piper, a great character to pair them with could be Sasuke. Sasuke's brooding nature and powerful skills would add an interesting dynamic. He could also learn a thing or two from Piper's magic.
One possible storyline could be Naruto finding himself in the Charmed Ones' world and teaming up with Piper to fight demons. Naruto's ninja skills would be a great asset against the magical threats they face.
One idea could be a crossover where Piper uses her magic to visit Hogwarts. She could interact with the students and teachers, perhaps teaching them some unique spells from her own magical world.
You can try searching on fanfiction websites like Archive of Our Own (AO3). They have a wide range of fan - created stories, and by using the search terms 'Piper' and 'pregnant' you're likely to find relevant fanfiction.
Harry Potter himself could be a great focus. Imagine him being introduced to the Halliwell sisters' way of life. His sense of justice and determination would be put to the test in a different magical context, and his relationship with Piper could develop in interesting ways as they learn from each other's magical experiences.
One popular Piper pregnant fanfiction might be found on FanFiction.net. You could search for stories that focus on Piper's pregnancy and how it affects her powers and relationships within the Charmed universe. Another place to look is Archive of Our Own (AO3). There are often many creative takes on this scenario in the Charmed fandom there.
Yes, there could be such fanfictions that are family - friendly. Some authors might focus on the emotional and relationship aspects rather than any inappropriate content. They could explore how Percy and Piper deal with the unexpected situation in a more innocent way, like how they face the reactions of their friends and family, and how they grow as characters through this new chapter in their lives.
One common theme is the anticipation and excitement around the new life. It often explores how Piper and the other characters react to the news of her pregnancy.