Some people have tried chelation treatments to strip heavy metals from the blood, but it stips other important elements and is quite dangerous. I've even read of children dying from the treatment - so don't get suckered into it.
Fish oil (or Omega 3's from other sources) is good for many things in the body, including nerve and brain function. I think everyone should take it, but it is especially important for children and those with autism. My daughter loves Barlean's liquid lemon swirl which is purified so the fish oil has no mercury or chemical sometimes in fish because of our polluted waters. Some people have reported benefits from it with their autistic children. (My daughter doesn't have it, but my friend's daughter does).
Here is info from Andrew Weil, MD site - www.drweil.com - he is a source I trust who uses both conventional and proven alternative therapies. In fact, he started an entire program of integrative medicine at Arizona University:
What therapies does Dr. Weil recommend for autism?
Some studies suggest that autistic behavior may stem from allergies or intolerances to the proteins in milk (casein) and in wheat and other grains (gluten). Limited research does show that some children with autism can't break down these proteins completely. Instead, fragments known as peptides get into the bloodstream and central nervous system before eventually being eliminated from the body. Several groups of researchers have identified these peptides in urine samples from children with autism. Some of the peptides are chemically similar to morphine and, in theory, may be the agents that cause autistic behavior.
It is well worth trying a gluten-and-casein-free diet to see if it helps a child with autism. Ample anecdotal evidence attests to marked improvement in some youngsters after foods containing gluten and casein were removed from their diets. Parents interested in exploring dietary approaches should read, Is This Your Child? by Doris Rapp, M.D.
Dr. Weil also recommend making sure that children with autism get sufficient omega-3 fatty acids. Recent research indicates that supplementing the diet with these beneficial fats can help address autism as well as depression, bipolar disorder, and attention deficit hyperactivity disorder. Good food sources of omega-3s include wild salmon, mackerel, herring, sardines and bluefish. Omega-3 sources other than fish are few: walnuts, flaxseeds, hemp seeds, and the oils extracted from them, and, to a lesser extent, soy and canola oils and specially fortified eggs.
Children with autism can also benefit from probiotics, products containing the helpful bacteria that normally inhabit the human digestive tract. Probiotics can decrease leakage of large molecules from the gut that can trigger immune reactions with effects on brain function.