there is a product my specialist put me on as i had low molybdenum (actually almost nil showing on a hair test), the supplement is called molyzinc (as its got zinc in it too). maybe it is worth trying short term in an extremely low amount, i'd be wary with doing anything long term in one this young but maybe you will see an improvement fast.
having my molybdenum supplemented, it only took 3-4 days before i got positive benefits from it.. i went from being unable to do maths at all in my head for years, to suddenly my brain able to do this hence i think it may be worth trialing a child showing a deficiency on a very low dose even if for only a couple of weeks. (for any long term supplementation of children, id be very wary.. go real slow/low and hair test again to make sure nothing is being overdone or better still find a professional to work with you with this).
my old dr told me that hair tests can be reliable as far as showing up deficiences go (but i guess that would depend on the lab doing the testing, the one i was going throu was a good one) . its other things that hair tests can be unreliable with them eg a hair test may show up too much of something which may be untrue..
If it was me, id trial supplementing with this rather then leave the child with a probable deficiency and molybdenum is an important essential trace mineral. and if you supplement dont do it forever, always keep checking things. (I have autism too.. aspergers, i dont know whether molybdenum deficiency showing on hair tests is more common in us or not but i ended up working out i had this deficiency due to a common gene mutation i have which came up on dna testing)