My son did that 1 time, when he was only 5... I taught him a lesson, and he never did it again....
he was writing his name on a white wall. in permanet black marker....I let him have a wash bucket with water, soap & a sponge. He washed for 2 or 3 hours....... the whole time I knew a spray of "hair spray " would take it right off..... He never did it again!!!!!
Hope it works for you too, Good Luck,
Karen