If you are thin and your winter is not too cold, you can have a pair of jeans. And men's jeans are not as thin as women's jeans. Although not very thin, jeans will be a little tight, so if you wear jeans, it is recommended not to wear them too thick. And jeans are versatile, no matter what kind of clothes you wear, jeans are ok. But remember, if you are not very thin, it is recommended not to wear jeans.
For boys who are a little fatter, I think it is better to choose a pair of sweatpants or casual pants. After all, sweatpants and casual pants are looser and more elastic than jeans. It doesn't matter if you are afraid of the cold. In fact, many pants are padded now. If it's not particularly cold, it's ok to wear only a pair of sweatpants or velvet casual pants, and it won't look particularly bloated.