ADHD and Learned behaviors

I had to go back to work and now my 18 month old todler has been under my sister's care for a couple of months now(from 8-4p.m).  She has 2 ADHD sons and my son has been spending quite some time with them.  AS of 3 weeks now, his behavior has drastically changed.  He has become violent and disrespectful.  He tends to hit his 4 yr old sister alot.  Can ADHD be a learned behavior that my son has picked up from my nephews?

[Kevin Kennedy, Ph.D.]

ADHD is not characterized by violent and disrespectful behavior. Now it may be that the behavior in the home of the relatives is not well managed and that too much aggressive behavior is being permitted. In other words, it might be that the parents are not setting limits very well. But it may also be that the change in your son's circumstances has him off his game. Such changes in environment can result in disorganized behavior and in a child as young as your son this usually takes the form of an increase in angry behavior.