If you are going to do "realistic" type stories in animation (I don't know why anyone would want to to, but that's all they seem to do), then you ought to learn something from live action. Real people are unique; they aren't all clones of each other like you see in animated features.
Here Pete Emslie took a bunch of the real child actors I featured a couple posts ago
http://johnkstuff.blogspot.com/2007/07/live-action-blands.html#comments
and did caricatures of them in an animatable style. (by keeping the details to a minimum and giving them some construction)
Pete's caricatures still have a somewhat Disney-esque look to them (without being all out Cal Arts style), all the kids have been cutesified, but it's a great first step towards breaking free from formula cartoon designs.
If I had really talented artists like Pete and some others, I would make them compete with each other to keep refining their characters and making them more and more specific-and combining different characteristics of different kids until we had something really unique and cartoony, so we weren't merely copying live action characters.
Some could be on the cute side, some on the funnier side. Variety and distinction is the key.
At Pete's site he explains in detail what his thoughts were:
http://cartooncave.blogspot.com/2007/07/bland-be-banned.html
As I said, if I was making a reality based animated feature, I would keep exaggerating and refining and doing variations of the designs until they become more and more specific and alive.
HOW "DEVELOPMENT" KILLS IDEAS
What usually happens instead in a feature studio, is the producers and executives keep shaving off all the unique parts of designs and personalities until the characters end up being the same old faceless, personality-less cartoon stereotypes.Harald Siepermann explains that creative process here:
Harald Siepermann's Clayton gets toned down by the Disney process