Children should start brushing their teeth as soon as the first tooth erupts, typically around six months of age. Parents should assist with brushing until the child can do it effectively on their own, usually around the age of 6 or 7. Flossing should begin when teeth start to touch, usually around age 2 to 3. Parents can encourage good oral hygiene habits by setting a positive example, making brushing and flossing fun, and providing guidance on proper technique. Regular dental visits also play a crucial role in reinforcing these habits and monitoring oral health.