Febrile convulsions
A rapidly rising temperature in an immature, seizure-prone brain can trigger a generalised seizure with no underlying intracranial cause, and the shape of the seizure (simple versus complex) is what predicts risk of recurrence and epilepsy, not the fever itself.
First principles
The immature brain is intrinsically more prone to seizure with fever
Between six months and six years, the developing brain has a lower seizure threshold than the mature brain, partly because inhibitory neurotransmission is not yet fully established. A rapid rise in core temperature (rather than the absolute peak) alters neuronal membrane excitability enough to trigger a generalised seizure in a susceptible child, without there being any intracranial infection, structural lesion or metabolic derangement driving it. The fever is the trigger, not the disease: the seizure originates from the brain's developmental stage, and the underlying illness is usually a benign viral infection.
Educational content pending clinical review. Not medical advice.