One reason could be that he's just a spoiled brat. Maybe he's used to getting his way at home and doesn't know how to act in a social setting like a party. Another possibility is that he's really insecure and acts out to get attention, even if it's negative attention.
Once upon a time at a party, there was a boy who was acting in a rather annoying way. People started calling him 'little bitch boy' because he was constantly whining and trying to get all the attention. He would run around and knock over drinks. No one really wanted to be around him, but he didn't seem to notice. He just continued his unruly behavior until finally, the host had to ask him to leave.
One possible reason could be that Santa's list got messed up. Another might be that the boy's house was hard to find.
Love. If the woman is the boy's mother or a close relative like an aunt or grandmother, the kiss is a natural way to show affection.
It could be out of natural curiosity. Little boys at a certain age start to explore their bodies.
One reason could be the author's desire to rewrite the relationships in a more edgy way. They might think that making Hermione mean to Harry will attract more readers who like drama.
One reason is to connect with others. By sharing her stories, she can find common interests or experiences with the party guests. For example, if she shares a story about her experience with a particular book, and someone else at the party has read it too, it can start a great conversation.
In the story, it could also be that the boy is trying to fit in with a group of girls. He might admire their activities or friendship and wearing the swimsuit is his way of trying to be part of their group. Maybe he thinks that by dressing like them, he can participate in their swimsuit - related games or just be closer to them. It could also be a way for the author to explore themes of gender fluidity or breaking gender norms in a child - friendly and innocent way.
One reason could be jealousy. Maybe the older boy has something they want, like a cool toy or is good at a particular sport. So, they bully him to make themselves feel better.
It could be to raise awareness about certain serious issues or to tell a powerful story that evokes emotions and prompts reflection.
Another reason might be as a form of self - exploration. Boys may want to understand what it's like to be in the shoes (or rather, the high heels) of the opposite gender, explore different aspects of identity, or simply break free from the traditional gender norms.