While I recognize the aforementioned 'limits of charity' when it comes to vulnerable children in Cambodia, there are several organizations doing good work in this area, with which every visitor to Cambodia should be familiar:

Mith Samlanh, or 'Friends', runs several business that train former street youth, including one of my favorite hide-outs in Cambodia: Le Café Mith Samlanh at the French Cultural Centre.

Child Safe Network is an international organization that oversees a variety of programs including anti-exploitation awareness campaigns and a reporting hotline.