Fish oil - high in EPA fish oil - has had some success in lowering risk of schizophrenia in people at high risk. I recommend you read this page and have your son take daily fish oil:
Preferably the composition includes about 700 mg of EPA and at least about 480 mg of DHA.
the … dose of EPA administered to the subject per day is about 700 mg and the final dose of DHA administered to the subject per day is 480 mg. The composition may be administered in multiple dosages over the period of the day. For example, 4 capsules may be administered over the course of the day (two in the morning and two in the evening). However, other administration (such as once daily, or twice daily) are not excluded.
Whilst it is possible that EPA and DHA be administered alone, it is preferable that they are administered together in a single composition. When in a single composition, EPA and DHA are present in a ratio of between about 3:1 and 7:5, preferably between about 3:2 and 7:5. Accordingly, preferably the composition includes EPA and DHA (when combined) in a concentration of more than about 50%, preferably more than about 55%, more preferably about 60%.
Read the full story here:
Also - I would give children a good dose of Methyl B12 - see this news story: