My question is about the quiz item: "El niño rubio con pantalones cortos es mi hermano."
Why was the article "los" not used before pantalones cortos? [e.g., El niño con los pantalones cortos es mi hermano.] An extension of my question here is that sometimes I notice a definite article is inserted while other times it is not. Therefore, what is the rule for using definite articles (los/las) in sentences of this type.