They're very easy to access. Once you've beaten the first group of levels, you'll be able to access community levels from the menu below the center planet. There are a bunch of search features now that I haven't played with much. But my daughter plays constantly. She's 7. There are some levels that are bloody/scary, but they're pretty uncommon. LBP allows you to report obscene levels, so you really don't stumble across them often. Other than a couple bloody levels, I haven't come across anything I'd keep her from playing.
You can choose to play any community level by yourself, or online with whoever might be trying to play the level at the time. I haven't run into any trolls or profane people online, but if that's a concern you can always have him play on his own (or with you!).