To put it straight, the answer is no. Darker tints do not block out harmful UV and are usually either used for reducing glare or just for fashion purposes.
Darker tints provide a stylish look
Darker tints do more harm than good because your brain thinks that you are in a dim environment and so your pupils do not constrict and you do not squint your eyes, therefore allowing extra sunlight into the eyes.
Sunglasses lenses are coated with a UV-blocking coating. According to an index called, The Eye-Sun Protection Factor (E-SPF), the higher the value of E-SPF, the better the protection against UV. E-SPF 25 means your eye is 25 times better protected than without any lens. Daily eyeglasses can reach an E-SPF index of 25 with sunglasses being able to reach 50.
Sunglasses provide a higher E-SPF index as compared to normal spectacles. （Images used is from the internet）
Things you should look for in a sunglass:
Even though polarisation and tinting are optional, they are recommended as they can help make your eyes more comfortable by reducing glare.
Amber and brown tints reduce glare and block blue light （Images used is from the internet）
There are also different sunglasses tint colour that serves different purposes. For example, Amber and brown tints reduce glare and block blue light. They brighten vision on cloudy days. And they increase contrast and visual acuity. They're especially useful against green and blue backgrounds, like grass and sky. Having Amber/Brown tinted sunglasses can provide children with clear and sharp vision whilst they go about doing their daily outdoor activities.
Rosy tints increase contrast by blocking blue light. （Images used is from the internet）
Rosy tints increase contrast by blocking blue light. They have a reputation for soothing the eyes. And they may be more comfortable for longer wear-times. Young children lack the pain tolerance that adults have and therefore they might suffer from eye-strain much easier after prolonged sunglass use. Therefore, a pair of Rose/Red tinted sunglasses can help give them a much more comfortable experience.
However, the tint colour of a pair of sunglasses does not affect its UV ray protection. When buying sunglasses, focus first on UV protection. Then, consider lens tints and what works best for you. You may find you like different ones for different purposes.
The Eyelet Sunplus is also available in small sizes that are designed for infants
Alternatively, Eyelet Sunplus is an option that parents can consider to provide their child with UV ray protection. The Eyelet Sunplus is a highly versatile form of UV ray protection that turns any child prescription spectacles into sunglasses in an instant. The Sunplus is specifically designed to attach itself on spectacle frames of different shapes and sizes. Designed to block out 100% of harmful UV rays, they are also scratch proof to cater to the rough handling of children. The Eyelet Sunplus is also polarised which will eradicate any unwanted glare to provide a comfortable wearing experience for your child.