You can autoload scenes or scripts.
If you autoload scripts, they usually don't have child nodes. They're just single nodes in the scene tree. You could add children programmatically but why?
Scenes usually consist of multiple nodes. In that content
get_child() makes more sense.
That said: I guess that you know that many people here successfully use
get_child. So you could derive that your problem is not very common. So how could you come to the conclusion that just your two sentences can help people narrowing down your problem?
If you need furthere help: Please define what you actually want to achieve and for what purpose you will use
get_child. And give us some idea of the node tree (parent, children, where script is attached...)which you expect to exist.