Poor little boy, and my heart goes out to you and your daughter. I think children especially, and rightly so, don't like the thought of anything being done to them. Our little son was the same about a lumbar puncture, had five nurses pinning him down and remembers it to this day. So not always soon forgotten.
I sometimes wonder whether we as a country are over testing at every little cough, sniffle, headache etc and especially in the case of young children who are often under the weather. I'm not suggesting it's a case of crying wolf too often because the very time we didn't test, sods law it would be covid. It's just that from a child's perspective it must seem like a truly horrible procedure with no benefits.
I hope you get a negative result back for him.