When your child borrows something belonging to the school: underwear (after your child's underwear gets soiled)
When you borrow something from the school, you should write a thank you note. In this case, you want to say thank you for borrowing the school’s underwear after your child's own underwear gets soiled.
Model
From the school
From the home
Conversational flow and useful expressions
Thanking the school
What you will do
Apology/gratitude
Parent's name
Supplement
For washing your child’s underpants, you can either thank the school with "arigato gozaimasu," meaning "thank you (for washing them)," or apologize with "sumimasen," meaning "I’m sorry (for having caused you extra work)."