My child just became afraid of the dark. How do I help?

Fear of dark. Children up to 6y have, 'magical thinking'. Tooth Fairy, Santa, etc are fun. The flip side, is belief in monsters. Treating magical thinking with magical thinking, works. I gave my daughter a charm, and told her the border in her room 'monster proofed' it. 'Magic monster spray' (air freshener) works, too. I knew it worked, when I heard her tell her sister that she was safe, since she had one, too.
Be supportive. Ask your child if there is something specific that scares him about the dark. Try to reassure him but use a nightlight until this fear resolves.