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There are lots of threads about this, but nothing beats just having frank and constant conversations about internet safety. If you are not good with computers, chances are that you will not be able to put a parental control on the computer that will fool a child for very long. My ds had hacked the parental controls at his elementary school when he was 8 or 9.
Ideally, long term, you want more than one layer restricting accessible material. For instance, our modem has parental control options built in, or you can make sure that SafeSearch options are set on UTube.
My DSs 7 and 4 regularly use laptops and iPad for games, browsing etc. My eldest son uses YouTube to download music videos and looks at things he is interested in such as pets etc. All innocent stuff. But there are no Internet controls on what he can access and I am aware that some need to be introduced swiftly.
So what do I do? I really have no idea. I asked at school and there were no help at all. Would really appreciate some advice and instructions from people more clued up than me.