A new study has shown that children as young as two understand basic grammar rules when they first learn to speak and are not simply imitating adults. The study also applied the same statistical analysis on data from one of the most famous animal language-acquisition experiments -- Project Nim -- and showed that Nim Chimpsky, a chimpanzee who was taught sign language over the course of many years, never grasped rules like those in a two-year-old's grammar.

Source: Young children have grammar and chimpanzees don't