The noun "traje de baño" (swimsuit) is the direct object of the sentence, and it comes after the indirect object pronoun and before the verb.
Here is a more detailed explanation of why "le" can be placed after "baño":
In Spanish, there are two general positions for indirect object pronouns (IOPs): before the verb (preverbal position) and after the verb (postverbal position). When the IOP is placed preverbally, it is usually placed before the direct object pronoun (DOP), if there is one. In this sentence, there is only one object (the traje de baño), and it is not a direct object pronoun, so "le" must be placed after "baño".
Here are some examples of how IOPs can be placed in different positions in sentences:
* Preverbal position: Me gusta la película. (I like the movie.)
* Postverbal position: ¿Me puedes dar el libro? (Can you give me the book?)
* Attached to the end of an affirmative command: ¡Ayúdame! (Help me!)
* Attached to the end of an infinitive: Quiero comprarle un regalo a mi madre. (I want to buy a gift for my mother.)
In this particular sentence, the indirect object pronoun "le" is placed after "baño" because there is no DOP. If there were a DOP, "le" would be placed before it. For example:
* With a DOP: Mamá le da un traje de baño a Juan para el viaje. (Mom is giving Juan a swimsuit for the trip.)