Gosh, I'd have to read some of my old stuff to remember how I RPed when I was a kid... I think things tended to happen without any real rhyme or reason 🤔 And definitely couldn’t use hard words (and if I did it's because I just learned it and wanted to show off 😝) 

Even in IRL there's times when the younger person acts infinitely more mature than the older person 😒 So it's also hard to just base it off behavior. 

I think the best guess I can make is what sort of slang they might use and if it's used as intended 😂