Of course, how someone appears as a new born baby and how they are once grown up can be completely different. The nickname sticks though, even if they no longer physically bear any resemblance to it.
Animals
Another common source is names of animals, or even from the sounds animals make. This tradition is also related to protecting the newborn child from the spirits, as calling the baby as if it were an animal was thought to be an effective way of tricking the spirits into leaving it alone. Some examples are: