40C (104F) is quite normal, specially in children. I believe what they say here is to seek help if you have 40C for more than a few days. Any thing above 41C (~106F) or if you’re in otherwise bad shape and it’s probably a good idea to seek help sooner.

People are different though, some will have 40C and be in fairly good shape, while others can barely walk as soon as they go above 38.5C.