Just want to ditto what everyone else said again. Like Trinity I am in the position of hiring many people as well, and in this economy, any thing can be a red flag to an employer. Anything.
I have practiced my "my son has a few challenges - you know the normal teenage stuff" speech until I am blue. However, even that, I only tell if pressed - and by law - no one can press you on that in the interview. In addition, like Susie said, no one can ask specifics of your past employer.
One last thing - even if you move there and they later find out that your son has problems and a PO - it will not matter - because you will already have the job. The key is selling yourself now - and worrying about the details later. Once you have the job, legally, there is nothing that can keep them from letting you go.