Yes, adults can buy Happy Meals at McDonald's. Happy Meals are not exclusively for children; they are available to customers of all ages. A Happy Meal typically includes a small, child-sized portion of a McDonald's menu item (such as a hamburger, chicken nuggets, or a cheeseburger), a side item (like apple slices or a small fry), a drink (such as apple juice or milk), and a toy.
While the Happy Meal is often marketed towards children with toy incentives, there is no age restriction on purchasing one. If an adult enjoys the smaller portion sizes, wants a specific toy, or simply wants to experience the nostalgia of a Happy Meal, they are welcome to order one at McDonald's just like any other menu item.