Parents have been urged to be alert to type 1 diabetes after the number of children presenting with symptoms fell by almost a third during the pandemic.
Between the end of March and middle of June, official figures show 33 children were diagnosed in Wales, compared to 48 during the same period last year.
If left untreated, children can develop life-threatening diabetic ketoacidosis.
One mother said she felt "so lucky" her eight-year-old son was diagnosed after she suspected a urine infection.
Trudi, from Chepstow, Monmouthshire, said she initially put changes in Harrison's behaviour down to the coronavirus pandemic and lockdown.
What is type 1 diabetes?
Type 1 diabetes is an auto-immune condition which causes the level of glucose in the blood to become too high.
It happens when a person is unable to produce enough of the insulin hormone, which controls blood glucose.
Unlike type 2 diabetes, it is not linked to age or weight. It can be treated by giving insulin injections.
"Type 1 diabetes can affect anyone," said Dai Williams, director of Diabetes UK Cymru.
"It's an auto-immune condition and it's just down to bad luck."
Experts have warned that anyone who is not diagnosed may develop diabetic ketoacidosis (DKA), a condition where harmful substances called ketones build up in the blood.
The condition is life-threatening if undiagnosed or untreated, although deaths among children are extremely rare.
Symptoms of type 1 diabetes include increased thirst, use of the toilet, tiredness and weight loss.
'We were so lucky'
Harrison, who was diagnosed in May, would get upset easily but Trudi thought it was because he missed his father and school friends during lockdown.
He also started to wet the bed at night, something he had not done since he was a toddler.
"He was drinking more, going to the toilet more, but it was hot weather and so I didn't think any more about that," said Trudi.
"But then the accidents happened more frequently. I thought it was a urine infection so I rang the GP."
Trudi was asked to take a urine sample at the surgery. Within minutes, the GP called her back and told her to take Harrison in urgently.
A simple blood test confirmed he had type 1 diabetes and he was taken to hospital the same day.
Trudi added: "We were so lucky. Harrison was diagnosed about a week before most children, when the symptoms get a lot worse."
Figures from the Children and Young People's Wales Diabetes Network show a 31.25% drop in diagnoses compared to the same period last year.
Doctors are worried it is because parents did not know the symptoms or were afraid to access medical services during the pandemic.
It might be too early to tell whether this is the case, according to Davida Hawkes, who chairs the network and is a consultant paediatrician at the Royal Gwent Hospital in Newport.
"It seemed that there was a lull in the number of children presenting, but when we look at the figures overall, perhaps they will be equitable when we analyse them at the end of the year," Dr Hawkes said.
"We believe that families have been nervous about making contact with the medical profession, either via the GP or coming to a hospital, for fear of the widespread nature of the coronavirus, particularly at the beginning of the lockdown period.
"We were concerned that families were not presenting their children who might have symptoms of diabetes."