A jelly baby was a type of confectionery that originated on the planet Earth.
It was shaped like a miniature humanoid child, made of gelatin and coated with starch. They were made in a variety of colors.
The Doctor was fond of them and offered jelly babies to James T. Kirk, Spock, Leonard McCoy and Montgomery Scott. Spock pronounced them "fascinating". (TNG - Assimilation² comic: "Issue 3")