Cherubs, or in the classical Hebrew plural cherubim, or the modern English pluralization of cherubims, all come to represent the same thing: high-order angels. Cherubim are less powerful only compared to the mighty seraphim, who are beings of such pure holy majesty that they exist only as radiant energy. Their sense of charity is so strong that they emit powerful rays of burning love. Typically in Orthodox iconography, seraphim are portrayed as heavenly disembodied heads surrounded usually by six powerful wings. Since the idea of iconography is to portray the idea of a religious being as opposed to documenting its exact features, a six-winged disembodied head is as good as anything to describe seraphim. A direct encounter with a seraph would likely de-molecularize a mere human.
So if cherubim are only slightly less powerful angels than the seraphim, how come they look like cute, chubby babies with wings? The answer lies in a semiotic drift that occurred during the Italian Renaissance. Properly, the winged babies are called putti (singular putto, meaning "little man"). The putti originate from ancient Rome, where they were associated with the gods at play. The putti eventually crept into Christian artwork, especially through the influences of the Great Master Donatello, roughly in the early to mid 1400's. There, the winged putti took their place alongside the powerful cherubim, and eventually the former supplanted the latter in popular culture.
Scholars are careful to point out that cherubim are sacred and putti are profane. That hasn't stopped the Vatican from collecting at least a million of the little guys and adorning almost every square inch of the Holy City with them.
For one thing, putti are fairly easy to draw, and for another, they can fill up a lot of space with images that are dynamic and pleasing. A painting Master would draw one or two examples, and then have his pupils fill the blank parts of a canvas or a fresco with their copies of the putti. They provide good student practise for coming up with poses and figuring out how to lay down skin tones using pigment. If an acolyte showed aptitude rendering putti, he could be moved on to more advanced models.
Although not very classical, I drew up these two poses as colour models for yesterday's cherub-tastic wedding card, which can be seen by clicking here. These models helped me visualize the renders I needed to lay out.