"Taking candy from a baby" is defined as something that is easy to achieve in wiktionary and many other sites. However, is our interpretation correct? Come to think of it, there are lot of things that are easier than taking candy from a baby. Similes such as "easy as falling of a log" would be something thats just easy to achieve, as nothing mean is involved.
A more appropriate usage would be doing something mean thats easy at the same time. Does it just reflect that being mean is so much part of everyday lives that we are just not thinking about it at all? Just take a look at this video, you will get an idea of how mean it really is. The baby will surely cry for a while. Taking candy from a baby sure requires a strong will and a stone heart.
It seems there is also an explanation that the origin of this simile has nothing to do with candies or babies. Its interpreted as taking C.A.N.D (abbreviation for a type of cargo)from Bay B of a ship. Since ships generally use Bay B as the sick bay, its impossible to locate it, let alone take the cargo out of it. So basically taking candy from Bay B was impossible. A linguist (April 1st joke) explains how the expression originated on board ships and got to mean something else after coming ashore.
We may never be able to prove if this is just a result of liberal attitudes towards being mean or the result of not having Bay B in ships.