I consider anything over 38 to be a decent temp, but I don't worry too much until it gets closer to 39.5.

As many PPs have said, it's more about the child themselves & how they seem, our worst scare was with Bubble who had a temp over 39 all day & was sleepy, unresponsive, wouldn't wake properly. Took him to the ER, they gave him nurofen & half an hour later he was sitting up on the bed singing songs the nurse actually called another nurse to 'come & look at this child now!'

If you're worried, it can't hurt to get it checked. hope he's feeling better soon.