Parents should ensure their children have their eyes tested within their first year of starting school following research that suggests millions have never taken them to the opticians.
Blind Children UK vision said screening is recommended to take place in schools for children aged four to five, but is not happening in two thirds of areas in England.
It has spoken to many parents who did not realise their child has sight problems as the child was too young to realise there was a problem and let them know.
Despite the fact that eye tests are free for under-16s, more than a quarter of the 2,000 parents (26%) who were surveyed for the charity had never taken their child to an optician.
Many were also unaware that eye examinations do not just test vision, but also look at the health of the eye.
"We are in a worrying situation where children are not getting their eyes tested either in school or at an opticians with their parents," Jayne George, director of fundraising and marketing at the charity said.
Tested within first year of school
"There are a number of eye conditions that are common among young children - some of which can lead to sight loss if not caught early - and these can be detected in a thorough eye examination.
"Early detection and intervention can make the world of difference, which is why we are calling for parents to get their children's eyes tested within the first year of school."
She said tests carried out on newborns only check the child's ability to detect light, and will not be able to ascertain whether their eyes are healthy and developing correctly.
"Growing up with a vision impairment can severely impact a child's confidence and development. Early diagnosis can help a child and their family to find appropriate support and in some cases, if caught early enough, can prevent an eye condition from developing enough to impact a child's sight," she added.
"If your child hasn't had a vision screening test at school, conducted by an eye health professional, we advise that you take them to the local optician."