It seems like good advice but optometrists also say that the wrong kind of lenses can also damage eyes and I fear the cheaper kids glasses may have that problem. So I think putting children in sunglasses that are effective my be cost prohibitive.
I also worry about children being boystrous and the potential for the glasses to break or for them to be lost.
I always wear sunglasses when I'm driving but not usually otherwise. They distort colours and I prefer to see things naturally, perhaps children would too.
If I had a child I would probably encourage good sunnies on very bright days ut not worry otherwise.