The translation su agrees in number with the noun which it modifies; their is translated by su, sus, depending on what follows: their father/mother su padre/madre; their books/magazines sus libros/revistas. For their used with parts of the body,
Here is a selection of useful words and phrases you will need in real-life situations while you're visiting Spain and other Spanish-speaking countries...
In Spain, a privately owned school that receives no government funds is called a colegio privado. Parents pay monthly fees. Colegios privados cover all stages of primary and secondary education.