I agree every parent should take their child for an eye test from the age of 4. DD is 5 and had one and is long-sighted but luckily doesn't need glasses yet but the optician recommended another appt in 1 year.
My parents never once took me for any eye test when I was a child, I was about 19 having my first eye test and guess what? I have a lazy eye and I am long-sighted no thanks to my parents. This is why I made sure DD had an eye test and I will do the same for DS when he is 4.
People seem to think that a lazy eye means they have a definate turn in the eye which is quite obvious but I can tell you this, you could never tell by looking at me that I had a lazy eye as it very rarely turns only when I am tired. But my vision in my left eye is crap even with glasses which I wear all day.
So yeah get your kids eyes checked.