One of the tricks, when you decide that you are ready to do something a wee bit more formal than than taking photos of the neighbour's kids is to realize what sorts of legal capers you can get wrapped up in with regards to photographing images that you don't own.

A quick search of the world results in some worthy discussion of legal releases, waivers, "get out of jail almost free" options. 

Photosecrets has a review of when you need to have your subjects sign a release. Dan Heller has a great article on when you need a release as well. That being said, if you are still not convinced, nothing beats having authentic legal advice.