IMC, elves are very whimsical creatures. Although they mature physically only half as fast as humans (meaning they look teenage from 30 to 40, adolescent from 40 to 50, and adult thereafter), their emotional maturity is much slower.
Simply put, elves are, naturally, barely above animals mentally. They don't think about consequences, and are preoccupied only by whimsy, curiosity, and the search for instant gratification. True sentience needs time -- and a lot of education -- to form.
By the age they're 60, they're mentally about like 10YO humans. Able to work and to be serious, but unwilling to. At this time, the elves start learning -- a difficult process -- those things that are essential to elven civilization. Trance, and martial training.
The trance is necessary because elves still have short memories. They live in the present, and are extremely oblivious to everything more than a week old. Through trance, they learn to remember lost memories, and to rekindle enthusiasm in old project, allowing them to fulfill them. The first trances of an elves are not a mean of relaxation, but are, to the contrary, exhaustive in the extreme. Only through time will they be able to master it until it can replace sleep entirely. (This is also this mental training that let them resist enchantment and sleep effects.)
Martial training is also an obligation. With all those devious but witless elven children around, being alert and vigilant is a necessity; to intervene in time when a foolish young gets threatened by a predator or a mob of orcs. Archery is especially great because arrows run faster than people.
For dwarves and gnomes, the explanation is different. Their physical maturity is only slightly slower than humans, however dwarves are required to do community services for a long time until they have symbolically repayed their debt toward the society. For 20 years, their community has taken care of them and given them education, food, shelter, and goods. For the next 20 years, they are required to provide the other dwarves with goods (crafting various stuff first, then leaving the sheltered halls for the first time and going on mining duty), food (working outside to hunt game, tend shrooms, or sometime work on the surface in some fields and orchards), shelter (joining the militia and protecting against marauders and beasts of the deep), and education (once they've done their time in all other duties, they prepare the next generation to perform the same duties).
Through these 20 years, the dwarf learned the bases of his trade (first class), as well as the various racial abilities -- stonecunning, combat techniques, etc.
Then, the dwarf is free to do what he wishes to, including leaving the dwarven halls and explore the wide world, or stay and enter a trade.
For gnomes, the deal is close to what it is with dwarves, but less spartiate. Rather than mining, gnomes spend time searching for alchemical plants and ingredients, learning to identify ingredients through its look and its scent; rather than crafting they learn the rudiments of arcane magic (I've kept the gnome cantrips as spells rather than SLA, they get three extra 0-level slots and spell mastery of dancing lights, ghost sound, and prestidigitation). They spend more time than dwarves gathering and preparing food (dwarves rely on trade a lot, and import about half of their food; while gnomes prefer to avoid depending on others), and they also learn the SLA to understand the animal language of burrowing mammals. Gnome family usually have a few foxes and/or badgers as pets; sometime even rats. (Given the gnomes' sensitive nose, they also spend a fair amount of time washing these odorous pets.)
Why wouldn't they? Keep the nasty waste off of everything that a baby touches, keep them from "streaming" into the ol' spellbook collection. An undiapered babe who hasn't been potty trained is a messy afair.
