Kids are often much more tech savvy then they think their parents are. But there are few gadgets today that don't offer parental controls to limit access to those undesireables. From DVRs to PCs to cell phones, the options are out there on how to add blockades for your children's access to adult content. It's not limiting freedom of speech, it's parents keeping some control of what and when their children are exposed to different information.
So here are some links on helping you find what to do to set up passwords, etc. on your preferred piece of technology:
Popular Cell Phones: http://www.pcmag.com/article2/0,2817,2336612,00.asp
Time Warner DVR: http://www.timewarnercable.com/corporate/answersondemand/parentalcontrol/blockingprograms.html
MS Internet Explorer: http://www.wikihow.com/Restrict-Web-Browsing-Using-Internet-Explorer