Fewer than one in 10 parents can identify the symptoms of Type 1 diabetes, figures suggest.
Just 9% of parents know that excessive thirst, extreme tiredness, frequent urinating and unexplained weight loss are all symptoms of the condition, according to a survey conducted on behalf of Diabetes UK.
The charity said that a lack of understanding about the condition is one of the reasons that a quarter of children with Type 1 diabetes are only diagnosed once they are seriously ill.
It has launched an awareness campaign to help parents spot the "4 Ts" which are symptoms of the condition - toilet, thirsty, tired and thinner.
Barbara Young, chief executive of Diabetes UK, said: "The symptoms of Type 1 diabetes are so obvious and pronounced that there is no reason why every child with the condition cannot be diagnosed straight away.
"But the stark reality is that a quarter of children with Type 1 diabetes become seriously unwell before being diagnosed and we need to bring this appalling situation to an end. I fear that unless there is a big increase in awareness of symptoms, we will continue to see hundreds of children a year become seriously ill completely needlessly.
"We need to get the message across that if you have a child or if you work with children, you need to make it your business to know the symptoms of Type 1 diabetes. We hope the 4 Ts will make them easier to remember and so help ensure children with the condition get diagnosed at the right time."
Former X Factor contestant Amelia Lily, who was diagnosed with Type 1 diabetes when she was three years old, is backing the campaign.
She said: "I feel very strongly that every parent and carer needs to know about Diabetes UK's 4 Ts campaign.
"My symptoms included drinking a lot more than normal and going to the toilet a lot. I was very lucky as my nana realised what was wrong with me because my uncle had been diagnosed with Type 1 diabetes when he was 14.
"It's so important that anyone who looks after children - not just parents but teachers, carers and other family members - knows how to spot the signs of diabetes. So many children are still getting really poorly before they are diagnosed and I want to help put a stop to that."
Type 1 diabetes, which develops when the body cannot produce any insulin, is an autoimmune condition that accounts for 10% of all cases of diabetes.
In the UK, there are 3.7 million people with diabetes, including an estimated 850,000 people who have Type 2 diabetes but do not know it.