At what temperature should I worry about a fever in a child?

What the evidence says

In Canada, a fever is a temperature of 38°C (100.4°F) or higher. Age matters a lot: the Canadian Paediatric Society advises that babies younger than 3 months with any fever should be seen urgently, and babies younger than 6 months should see a doctor for a fever. For older children, home care is usually fine as long as they're drinking well and otherwise seem okay, but they should see a doctor if the fever lasts more than 48-72 hours.

For children of any age, the height of the fever itself is not the best way to judge how sick they are — a mild infection can cause a very high fever, while a serious infection sometimes causes little or no fever. What matters more is how your child looks and acts: alertness, activity level, and whether they're drinking fluids and making urine normally. See a doctor or seek urgent care regardless of the exact temperature if your child has a stiff neck, a rash that doesn't fade under pressure, is very hard to wake or unusually limp, has trouble breathing, is refusing fluids or showing signs of dehydration, has a first-time seizure with fever, or just seems seriously unwell to you as a parent.

HealthLink BC (811 in BC) and similar provincial telehealth lines can help you decide if you're unsure. Canadian guidance differs slightly in emphasis from some U.S. sources, which sometimes give more specific temperature cutoffs for treatment; Canadian sources consistently focus on age and how the child looks rather than a strict number for older infants and children.