Funny you should ask to have it explained like you were six years old; here's an explanation like you were five years old :)
everywhere I look I see a push in the direction of containers such as Castle Windsor
Frankly, I think the reason for that is that most people actually don't understand what Dependency Injection is, which means that instead of grasping the concept of Inversion of Control, they go looking for a replacement for the new
keyword they're already used to. Then they find a DI Container and (mis)use it as a Service Locator. Unfortunately, that's very easy to do.
This is the reason why, in my book, I explain all the DI concepts without coupling the explanation to any single DI Container. That's actually the majority of the book.
Service Locator and Dependency Injection are two fundamentally different attempts at achieving loose coupling. Service Locator has many disadvantages, and offers no advantages not also offered by DI. This is why I think it's safe to call Service Locator an anti-pattern.
You don't need a DI Container to use DI; in fact, I would say that unless you take a rather sophisticated approach, it's probably better to avoid one.