On the purely technical side, there are a few things you can do to protect yourself from such things. You can easily use pop-up blockers, most of which are available free online. Better than that, even, is using a different browser. I use Mozilla, and it is set so that any window I don't open myself either doesn't open at all, or is blank when it does. This might not work on aol...It's been a long time since I was on there, so I don't know what they let you do on their service.
Your homepage can be reset, but not always exactly without your permission. Most people click windows closed so fast they don't realize what they are pressing. You can very well agree to something without noticing it.
Clear out your cookies. Install ad-aware, a free program that searches your computer and finds and spyware which can then be easily deleted.
Child porn is easy to find because the internet is international. Most of these places are hosted overseas, so American law doesn't apply. And it shouldn't. Some countries limit what can be found in their search engines. I believe it was Yahoo! China that disallows certain anti-governmental websites from showing up. You could make your own search engine, I suppose, or perhaps there is a porn-free one somewhere.