>> How do you keep young children who have access to crayons and markers from decorating your house?<<
Keep the coloring supplies where he can’t reach them so that you need to give them to him when he wants them, and supervise him carefully when he uses them. Immediately intercept him and matter of factly remove whatever he’s using as soon as you see him about to use the crayons or markers inappropriately. He’ll realize very quickly without you saying much that if he wants to use them, they will have to be used in the right way.
Isn’t it nice to have an issue that’s so easy to resolve?
Avivah
While I was in the hospital having my 6th baby, his next oldest sister (almost 3) took the opportunity (with Grandpa in charge) to decorate the stairwell wall and carpet with whiteboard markers! We eventually had to replace the carpet and use several coats of paint on the wall. She still remembers the long period of time she wasn’t allowed to use markers!