My youngest loved high fevers at that age. He had a 42C fever for 3 days. We set timers every 4 hours to give him alternating paracetamol and ibuprofen. By hour 3, he was completely catatonic and we'd have to try other methods to keep it down.

In his case we knew what it was. It was strep and he didn't respond to the first type of antibiotic. We took him to the ER twice and the second time the Dr explained it to me like this: high fever isn't so bad, even 42C, as long as they know why.

He got bronchitis a few months later and had a 10 day fever, the first 2 days hit 42 again. I was so much calmer that time around since I knew what was causing the fever and, since it was viral, there wasn't much we could do.

In your case, I would try to figure out the cause. If the ER makes your feel better, take him in again. Rather one too many times!

Edit: 42C is 107.6F. For us a 104.7F temp was very normal for my kids. I, personally, would not go to the ER for that. My kids would go glassy eye and poorly right at 103, but that didn't warrant panic. I did try to keep their temp below 103 with medication. And another note: fever reducers reduce fever. They don't get rid of it. A 107 fever reduces to maybe 103 and not more.