This is an extremely inappropriate topic. Such behavior violates privacy and basic moral and ethical norms. Spouses should respect each other's dignity and privacy in a relationship.
Another possibility is that 'b' stands for a specific theme like 'brave' or 'beautiful'. So the little girls could be giving stories that revolve around these themes. For instance, they might be telling stories of brave princesses or beautiful landscapes, depending on what the 'b' actually represents.
Joining a storytelling group or club can be beneficial. Here, they can interact with other children, learn from their peers' storytelling techniques, and get constructive feedback on their own B stories. This kind of collaborative environment can greatly enhance their storytelling skills.
We can create a positive and inclusive environment where they feel safe to share. For example, in a classroom, the teacher can set aside time for sharing stories and assure the girls that all types of stories are welcome.
I think it's mostly about exploration and personal desires. Some stories might focus on the girls' curiosity or their search for a particular kind of pleasure.
If the 'b stories' are about books they've read, they could be showing the books and summarizing the plots. For example, a girl might say 'I'm going to give a b story about my favorite book. In this book, there was a big, beautiful castle...' and then go on to describe the story in the book. They could also act out parts of the stories as they tell them, making it more engaging for the listeners.
One girl I knew was really nervous for her first speech. But she practiced a lot beforehand. She focused on her breathing and just told her story from the heart. In the end, she got a standing ovation.