HI, and welcome
We use Omega's and Vitamin E, and magnesium( be careful with magnesium, to get enough you almost have to cause diarrhea- Milk of Magnesia is magnesium)
They do take 3-4 months to see results,and do not help focus...they are mostly for moods.
A child may HAVE ADHD, but it is not what they ARE. Never tell a child they ARE ADHD.
You should read "Healing ADD" by Daniel G. Amen, MD. He believes (based on brain scans) that there are 6 types of ADD/ADHD. He lists different supplements and diet changes that can help with each type of ADD (as well as the correct medications, as stimulants do not work for all types. Just information in case supplements/diet don't work well enough for you.)
Just in case you want to look into it, my son was recently diagnosed as ADHD by a neuropyscologist. (No brain scans though.) Right after the testing, we started doing vision therapy because I had noticed that my son was skipping over words, flipping letters, and reading last words first. The optometrist confirmed that his eyes were not tracking together properly for reading. The interesting, and relevant to this discussion, is that his distractibility, impulsiveness and movement in general, has gone WAY down. (Still, he may be considered ADHD - we homeschool so it doesn't matter so much to us.) I think that he had to move to see things clearly (so that it wasn't double vision,) which gives the impression of ADHD. I am NOT saying this will work for everyone, but if you see other issues like my son had, this may be something to check out as it is a no medication way of treatment. Incidentally, we are half way through, and he is not reading much better, but that should come. We are not doing medication either, but have modified diet a little to add more protein, especially in the mornings. We will try supplements after we finish the vision therapy if still needed, but I did want to try one thing at a time so that I know exactly which thing is the thing that "works" or not.