Kid: c.1200, “the young of a goat,” from O.N. kið “young goat,” from P.Gmc. *kiðjom (cf. Ger. kitz). Extended meaning of “child” first recorded as slang 1599, established in informal usage by 1840s.
Yes, that’s true… and they were called ‘kids’ long before children and young people were called ‘kids’. In fact, that’s where the name originated.
My mother would never allow me to refer to children as ‘kids’. I still don’t.