Watching Avatar for the 39th time, I realized a subtle detail early on. In the extended version, Grace says that the Na'vi children were “so eager to learn. They picked up English faster than I could teach it.” Another instance, Norm says that the avatars fully mature on the 6-year flight to Pandora, referring to both the physical and cognitive development. It’s never explicitly stated in the film, but Jake’s avatar is about 17. I don’t know about you, but most 17-year-olds aren’t fully mature in either category.
The Na'vi children have higher cognitive potential. In other words, Na'vi children learn faster than human children, apparently understanding homophones and homonyms as well.