It might be a family tradition. In some families, boys are given special nightgowns to wear as part of their bedtime routine. It could also be that the boy saw someone else wearing a nightgown and thought it looked cool, so he wanted to try it too. Another possibility is that the nightgown was a present from someone he loves, and he wears it to feel closer to that person.
Perhaps the boy is in a play or a costume event where he has to wear a nightgown. Or it could be that he's staying at a place like a boarding school or a camp where the uniform for bedtime is a nightgown. Also, if the story is set in a different time period, for example, in the Victorian era, it was more common for boys to wear nightgowns, so it could be a historical context thing. And let's not forget that some boys might just like the feel and look of a nightgown and choose to wear it on their own accord.
Well, there's this boy wearing a nightgown. He might be wearing it because it's comfortable. Maybe it was a gift from his grandmother. He could be walking around the house in it, feeling all snug. He might even do some activities like reading a book while in his nightgown. It could be a plain white nightgown that makes him look like a little angel in the early morning light when he gets up to look out of the window.
There is also a possibility that the boy is into figure skating. Leotards are often worn in figure skating as they are sleek and don't restrict movement on the ice. He could be at the skating rink, training hard for a competition.
In some stories, the boy could be wearing a diaper for a role - play or pretend situation. For instance, a group of kids are playing 'baby day' and a boy named Alex decides to wear a diaper as part of the game. He wants to experience what it's like to be a baby again, and he has a lot of fun toddling around in the diaper, pretending to be a little infant.
He might be simply playing and exploring. Kids are curious, and wearing something as different as mom's boots is an adventure for them.
Maybe the aliens are just curious about human beings' reaction to tickling. They don't understand our emotions well and want to see how we respond when tickled.
One possible plot could be that the boy is a young toddler who is on an adventure in his backyard while wearing his diaper. He discovers a little bug or a small animal and tries to communicate with it, and his diaper becomes a part of the comical elements as it might be a bit bulky or get dirty during his exploration.
Perhaps he is in a play or a theatrical performance where he has to wear a skirt for his role. This could lead to interesting interactions with his peers who might initially be surprised but then come to understand the context of the performance.
It could be for a school play or a performance. The boy might have been cast in a role that required him to wear a girl's swimsuit for the sake of the story or character he was portraying. For example, if the play was about a mermaid and they didn't have a proper costume for a male mermaid, they could have used a girl's swimsuit as a creative solution.
One significance could be for comical effect. It can make the audience laugh when a boy is dressed in a saree, especially if it's part of a mistaken - identity plot. For example, if he's mistaken for a girl due to the saree.
One reason could be a lack of awareness. For instance, if a young boy is just learning about clothing differences and accidentally puts on panties. Another could be in a situation where there is a mix - up in laundry. Maybe all the clothes were jumbled together and he unknowingly picked out panties. It could also be part of a magical or supernatural story where some spell or curse causes him to be in such an unusual clothing situation.