I think that trying to lower a fever with cold towels is pointless. If your body decides it wants to be 40°C / 104F then it's going to do everything to maintain that. So by trying to cool the body with wet towels, you are just making it work harder, and you exhaust the kid even more.

Anti inflammatory drugs like Ibuprofen are the most effective way of lowering fever, it will actually cause the body to cool down on its own, and no wet towels will be necessary. Unless you have a really severe infection, in which case you should go to the hospital.

The only time when wet towels make sense if your kid can't regulate body temperature on its own anymore (eg. because of severe dehydration), but then you should really take them to the hospital as well.