Overprotective parents inhibit more than their kids' freedom: they may also slow brain growth in an area linked to mental illness.
Children whose parents are overprotective or neglectful are believed to be more susceptible to psychiatric disorders – which in turn are associated with defects in part of the prefrontal cortex.
http://www.newscientist.com/article/dn18633-mom-and-dad-stop-stifling-me--its-damaging-my-brain.html