According to Deadspin, seems like its being implied the club got tired of having to act as babysitters for the kid because LaRoche was way too laid back when it came to taking care of him in the clubhouse.
White Sox didn't have a real problem with the kid being around or running some errands to "earn his keep" but probably didn't want to be on the hook for any legal issues in case anything bad happened because of LaRoche's care-free attitude with him in the clubhouse.
http://deadspin.com/adam-laroche-ret...let-1765311014