How can I animate children with their own animation controller

I'm animating an intro animation to a scene. The problem is the animation will have parts that will have their own animations running once the intro is finished and the scene is running normally.

It says here near the bottom that I should be able to animate objects with their own animator. Acording to the picture I have to just select the controller. But I don't have that selection. The moment I click on an object with its own animator it switches controllers and only lets me select the animations in that controller, not switch controllers.

How can I animate children when their controller overrides the parent's in the animation editor?