I'll sum up the main points instead. Most of you said that cookie comes from a program invented at MIT around 1970 called 'Cookie Monster' after the cookie monster from Sesame Street. It extended in sense from there to Web browsers and other programs. A lot of you think that 'cookie' is a shortened form of 'magic cookie'.
Tokens is perhaps a better term.
In some ways a cookie is like a Passport that gets stamped as you enter various territories. Cookies are something a server gives to a client. And the client may show the information back to the server on subsequent pages, actions or visits. However, it may have strings attached - you only get a cookie if you are good. So the child is being bribed.