The warning not only hit home to many parents, but has also encouraged one mother to come forward after spotting the cancer through an iPhone photo.
Photos taken on iPhones can sometimes show a sign of retinoblastoma (Rb), a type of cancer where tumours develop in the eyes of babies and young children.
Stacey Sutherland took a family snap of Zak when they went for a trip on the Polar Express train ride in December and noticed whiteness on the photo in his left eye.
Sutherland's 20-month-old son had already developed a squint and she had made an appointment for him to be seen by a consultant, and was due to be seen in April.
But armed with the smartphone picture, she pushed for an earlier meeting with specialists who diagnosed retinoblastoma - a rare type of eye cancer that affects under-fives.
Up to 50 children a year in the UK are diagnosed with it and 98% are successfully treated, according to NHS figures. But many need to have their eye removed to save their life.
Mrs Sutherland and husband John, who also have Evan, six, Tyler, four, and Jonah aged three, have been told early diagnosis has saved Zak's eye.
He has undergone chemotherapy and laser treatment, and is under the care of the Royal Victoria Hospital, Newcastle, and the Birmingham Children's Hospital.
Mrs Sutherland said: "If you take a picture from a 15 degree angle it can catch the optic nerve which shows up as a peachy colour, but this showed up cloudy white, and that was worrying.
"This kind of tumour grows quite quickly and if we had waited he might have lost his eye."
She added: "If you are concerned, get it checked. It doesn't take much to determine if there's something wrong.
Childhood Eye Cancer Trust (CHECT) chief executive Joy Felgate said: "Retinoblastoma is a very treatable cancer but is often diagnosed too late to save a child's eye.
"This is mainly because parents don't have the information which could lead them to seek help earlier.
"It is vital that every parent is aware of what to look out for so that should their child, or perhaps a friend or relative's child, display any of the signs of this eye cancer, they would recognise the need to seek urgent medical attention as early as possible."
CHECT medical adviser Ashwin Reddy, consultant ophthalmologist specialising in retinoblastoma, added: "Although this cancer has a very high survival rate, many children live with the consequences of a delayed diagnosis.
"This can mean loss of one or both eyes, an artificial eye, a visual impairment or, in some cases, complete blindness.
"In unilateral cases, 70% of children will need to have their eye removed to save their life."