It depends on your budget. Clip on sunglasses can be customized for children, but they are quite unaffordable. Fortunately, there is a good alternative for these bothered parents. Photochromic lenses can also provide UV protection which are much cheaper than Clip-on sunglasses. In conclusion, this type of eyeglasses eliminates the extra expense of sun clips yet still guarantees UV protection and eye safety.
Get them photochromic glasses. If they don't lose the clip-ons, they'll forget to use them. Photochromic lenses might cost more, but they'll have one pair of glasses that they can wear all the time while still having sunglasses as needed. Since they work automatically, you can guarantee that they have the protection when needed, and since they'll be wearing one pair 24/7, you know they won't be lost.