I did searches to make sure that nothing like this had been suggested yet.
When a baby falls off of a bed, it's OK. When I child is shot in the arm, it will heal. Neither is the case with an adult. An adult will have a headache or some other pain after falling out of bed. An adult's arm may heal after being shot, but it will never work the same again. Any parents will notice this about their toddlers, who get into so many scrapes and accidents. I myself CRACKED my skull OPEN when I was four years of age... and now I only have a small scar on my forehead (that has constantly been related to Harry Potter, we're friggin twins. Other than that I'm a mostly black girl, rather than a scrawny European boy)
The truth is that the younger you are, the higher your regenerative capabilities are. That is not limited to just human, it happens with ALL life forms that are not completed developing. Life does not evolve after development is completed, it happens BEFORE. I'm no doctor, so I'll post some links to articles about it for now:
http://health.howstuffworks.com/children-bones-heal-faster.htm,
http://www.gdrc.org/kmgmt/learning/child-learn.html And of course it isn't limited to the physical; it's FAAAAAAR easier to learn as a child than as an adult. Most mental devepment is during youth.
My suggestion after all that writing is this: Dwarven babies should be mostly immortal. Their injuries should take 1/4 the time to heal as an adult. If one of their lungs are punctured, it shouldn't be a sure death. It should be a guaranteed OK. Of course a severed head means death, but a severed arm will not kill the baby dwarf from loss of blood. And learning; baby dwarves should gain more experience from any tasks that they complete than a mature dwarf. I know that baby dwarfs don't do a lot, because they're always in their mother's arms. But what about swimming? A baby dwarf who's mother wander into 5/7 water may drown, but her baby should gain experience quickly enough to live... right before it attempts to commit suicide off of a cliff. And there's another thing! It shouldn't be so easy for babies to commit suicide, they should be harder to injure and faster to heal. (But none of that will matter if your Dwarf civ is modded to [SPEED:1], since it can injure itself faster).
THERE MUST BE NO SURVIVING FIRE, MAGMA, A COMPLETE ARMY OF GOBLINS, OR 3 Z-LEVELS OF WATER!. All this immortality will weaken after one year; when you baby dwarf becomes a child. CHILDREN CAN GATHER! Urist McChild should gain a lot more experience from gathering food from the farm than his/her parents. By the time adulthood is reached, he/she should have a definite job opportunity, rather than a Dabbling Gathering skill.
Please add to my suggestion and discuss balance.
