What is a kid? Good explanation needed.

A kid is, in a broad sense, a minor under the age of 18. In a more narrow sense, a kid is anyone who isn't considered a teenager, usually under the age of 13. In a more symbolic sense, a kid is someone who's innocent, vulnerable, and worry/stress-free.

tending to cause harm

hm, switch the relative; nominative and indefinite; objective ? not too bright in the knowledge of the english.