What is Bruno's relationship with Maria?

Maria is Bruno's family's maid.

One afternoon, when Bruno came home from school, he was surprised to find Maria, the family's maid - who always kept
her head bowed and never looked up from the carpet - standing in his bedroom, pulling all his belongings out of the wardrobe and packing them in four large wooden crates, even the things he'd hidden at the back that belonged to him and were nobody else's business.