The problem with the App Store, is that the software most likely to have an issue with the sandboxing is often the software that's more critical in terms of security. Such software may not be security software but still have more stringent needs in terms of security review. For example, layout managers might have hotkey functionality that could disguise key-logging.
Your typical "parents" are not the sort to need that sort of stuff. Those are profesional tools for people with specialized needs, and they can assess the risks of installing such things.
