As a quick and dirty young'n stats. If the average Attribute rating for humans is 3, then average for around puberty (12 years old +/1 2 years) would be 2, and prepubescent is 1. If I remember correctly human physical maturity is reached around 20 years of age (younger for women, older for men, averages to ~20). Though doing a quick search on the subject there doesn't seem to be a consensus on this and the only thing that's certain is when puberty is reached and that depends largely on environment, diet, society as well as some genetics and add to that women start puberty earlier than men...on average.
So my ad hoc average human attributes by age would be
| Ages |
Attribute | <7 | 7-14 | 15-20 | 21+ |
Body | 1 | 2 | 3 | 3 |
Agility | 1 | 2 | 3 | 3 |
Reaction | 1 | 2 | 3 | 3 |
Strength | 1 | 2 | 3 | 3 |
Charisma | 1 | 2 | 3 | 3 |
Intuition | 1 | 2 | 3 | 3 |
Logic | 1 | 2 | 3 | 3 |
Willpower | 1 | 2 | 3 | 3 |
(I did the table because I thought, hey, I bet there's some mental attributes that could be adjusted differently, or even like agility or reaction reaching 3 earlier than others, but then looking at them, and realizing that these are inherent averages (and to keep tracking these things to a minimum) the 1, 2, 3 progression works just fine even though saying a 15 year old has the same developmental level as a 25 year old, physically and mentally, doesn't sit quite right with me. And the differences between a 7 year old and a 14 year old are quite huge. So maybe doing it as <11, 12 - 15, 16+ as the 1,2,3 would fit better for actual game play.)
Then, after adjusting for sub-species ages (orks and trolls maturing hitting puberty early than humans etc.) I'd use those same categories and for the <7 range give the species-bonuses to attributes at 1/2 or even 1/3 maybe, then 7-14 at full or 1/2, and full attribute bonuses after 15.
And of course a whole range of negative qualities could be / should be layered on as "inherent" for the various ranges. Like <7 would be uneducated (don't have my book here so I can't go through them, but I know there's more that would fit an average 5 year old, hehe, like Uncouth - saying what's on his or her mind with no social control, picking noses, throwing tantrums, etc.). And so on.
Otherwise...yes, including children in the game, especially as enemies, brings a level of dark to an already mostly-dark game (NERPS!). For a fantasy game I was going to run I did my own age categories for the various species and included average stats for them (stats based on age category and species). I showed it to a fellow gamer and he just asked "why? Why include this. I mean, having the stats for a 1 or 4 or 8 year old is just extra work you don't need to do, because really who's going to want to play in a situation/encounter where you have to worry about the stats of a kid, or an infant even. I mean, if it comes down to it and we have to try and save the kid but the monster gets there first...the kids dead." This hadn't even occurred to me...I just like statistics and seeing how to make a world somewhat internally consistent within the rules.
On the otherside, I did start a campaign where the PCs were just post-pubescent, living on the edge of the barrens, and having to find their way in the world. I did the campaign with two different sets of players. One didn't take to it. The other did. The one that took got into it, the mage used a pokemon deck as a source for inspiration for his character's abilities, the other a technoshaman playing games, etc. Then slowly introduce elements to pull them into the shadows. A ghoul that wants to bring the kids into his organlegging gang, another "standard" street gang, a P.I. that would use the kids to keep an eye on targets, the Lone Star cop that used them to get info on anything going down, etc. It didn't last long, but that was mostly because of other events. My plan had been to "have them grow up" into 400 BP equivalent adults over the course of about 4 - 8 missions.
