If you mean N-acetyl cysteine, it's a glutathione precursor. Glutathione is an important antioxidant critical to liver function, among other things.
Milk thistle (as a supplement) is a popular glutathione precursor. There are others but I don't remember them because milk thistle worked for me, so that's what I used.
I don't know. I'm not a child. I didn't give it to my children.
If I were trying to help a child, I would likely start by removing particleboard furniture and other sources of off-gassing from their environment as a means to lighten the load on their liver.
Though to be frank, I did that for me as well, on top of supplements because I was very sick at the time.
There is some limited evidence that NAC can be effective for treating severe COVID-19 symptoms. However, I don't think it has been incorporated into any of the official treatment protocols.
Milk thistle (as a supplement) is a popular glutathione precursor. There are others but I don't remember them because milk thistle worked for me, so that's what I used.