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.
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.
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 bullying at school. Other kids might pick on him because he's different in some way, like being too shy or having an unusual hobby. This can make him feel really sad and isolated.
There could be many reasons. Maybe he ran away from home because of some family problems. Or perhaps he was lured away by someone promising something exciting. Another possibility is that he had an accident and ended up somewhere unknown.
It could be out of natural curiosity. Little boys at a certain age start to explore their bodies.
One possible reason could be that Santa's list got messed up. Another might be that the boy's house was hard to find.
One possible reason could be for a medical condition. Maybe the boy has a physical disability or a medical issue that requires him to be in a diaper for a long time and some situation led to him being locked in a room while in that state. Another reason could be a form of punishment in a very cruel and inappropriate scenario which is of course not acceptable in normal circumstances.
It might be a form of self - expression. In modern society, fashion is becoming more inclusive. The boy could be expressing his unique sense of style or challenging gender norms by wearing a skirt. He may want to break free from the traditional idea of what boys should or should not wear.
One reason could be for a school play or theater production. For example, if the play requires a male character to disguise as a female for the plot. Another reason might be part of a bet or a dare among friends, just for fun.