list of category from parent category

dear
i create a template for opencart for specific site.
i have 3 parent category and i have 3 box in home page that each one show subcategory of each 3 parent category.
as example i have this parent category :
cd --> parent id : 35
dvd --> parent id : 40
blueray ---> parent id : 45
i want to show subcategory of this category in home page in a list.
what should i do ?