@hazlin >at 100F you have a fever, and at 101F you have a bad fever. If you go above that, it is time to take an ice bath.
It is much easier to remember that at >38°C you have a fever and >40°C you have Hyperthermia, as that's 2 rather than 3 digits to remember.

>Simple enough to remember in a crisis, and save your child.
Knowing that >=40°C that an ice bath and following medical treatment is required is slightly easier to remember than a 3 digit number.