I look at the symptoms on top of the temperature. That's partially because dd2 had a tendency for temperatures of over 40 (over 41 on occasions too) and would still be dancing round and bouncing, whereas the other two would be wiped out by the time it got to 38.
What I look for:
Firstly when you first notice it, how are they in themselves. Are they refusing food? Not to worrisome. Refusing drink, that's not good. If I offer them a treat drink with a straw and they refuse it (or an ice lolly as another treat) then I'm onto keeping very watchful.
Are they vomiting? Once, no worries again. Second time-is there a reason-just gulped a glass of water/bouncing on the trampoline (yes dd2 would do that with a temperature of 41 if allowed)/ate a bite of toast... Otherwise how frequently are they being sick?
If they're sick every half an hour, not drinking and temperature up, that's when I start worrying.
Next thing is a do get them to move their neck (chin to chest) and check for rashes. Don't panic, even with a non-fading rash as viruses can cause that as I have found out through a ds who gets viral rashes very easily and many blood tests in A&E with them.
Are they complaining of anything else? Too young to tell you, took at how they react to you. Do they want to be touched, held etc?
Then what do they want to do? If they're down on the floor pushing a car around then they're probably fine. A really ill child won't have the energy for that. only time we've nearly been blue lighted was when ds was at the doctors and he wanted to play with the cars but didn't have the energy to crawl across the floor, just lay there with his head down.
Then what happens when you give calpol/ibroprofen. Yes, I know people will say don't use it to bring down fever, but you know what, if I have a temperature I ache and would give myself pain relief. I think children are the same.
So give it, take temperature. Take temperature about half an hour later. Has it gone down? If not, try again in an hour.
If it hasn't gone down at all, then I would start worrying unless that is typical for the child . But combine that with how they are behaving, if they seem to be getting worse etc.
And do bear in mind that temperatures do seem to have a tendency to rise at about 2am. My doctor agreed when I said that. Coincidentally that's the time they shut the out of hours at our local hospital for a couple of hours.... 