three-nager
n.— «Whoever invented the word “three-nagers,” was clearly speaking from bitter experience—they were describing three year olds with the rebellious spirit of a teenager, but none of the reasoning skills!» —“House Of Tiny Tearaways” TV One (New Zealand) Apr. 9, 2006. (source: Double-Tongued Dictionary)
Further reading
There was a time when William Shakespeare was just another little seven-year-old in school. Classes in his day were demanding — and all in Latin. A new book argues that this rigorous curriculum actually nurtured the creativity that later flourished...
Wilson in Charleston, South Carolina, stopped using the term conversate after being told it’s not a real word. On the contrary, conversate is well-established in Black English as a verb that suggests speaking in a register that’s warmer...