* गृहकार्य (Grihakarya): This literally means "home work," and is the most common and generally understood term. You could specify it as "छुट्टियों का गृहकार्य" (chuttiyon ka grihakarya) for "holiday homework."
* अवकाशकालीन गृहकार्य (Avakashkaleen Grihakarya): This is a more formal and literal translation, meaning "vacation time homework."
* रजनीति गृहकार्य (Rajniti Grihakarya): If the holidays are specific school holidays like summer vacation then this would be better option meaning "School Holiday Homework"
The best option would likely be छुट्टियों का गृहकार्य (chuttiyon ka grihakarya) as it's clear, concise, and easily understood.