The chart at the end of this article gives a ballpark for ability stats. I've streamlined age groups for simplicity. I also included a simple guide for approximate heights and weights (human), assuming no difference between male and female. These numbers should be modified to reflect general body type (muscular, tall and skinny, or short and fat, etc.) and race, obviously. Heights and weights are listed in US inches and pounds, or Metric cm and kilos.
Ability Stats Min/Max: I've kept Intelligence and Dexterity a bit higher than other stats, while scaling down Wisdom significantly. Charisma remains the standard 3d6 (or whatever cheating method) because it is entirely subjective and completely in the eye of the beholder, especially if all the heroes are youngsters: it's either "Mr. or Ms. Personality" or "Oh, he/she's cute like button!" Whatever. Feel free to dole out reaction penalties when youngsters meet dour old fogies.
Prerequisites and Prime Requisites: These vary with the game version. In Basic D&D, there is no minimum to qualify for character classes (just use the score rolled). In other D&D versions, minimums may require scores of 9 or more. In this case, if the score is too low, change it to the minimum required in the rules. Personally, I hate the latter approach. I'd much rather use whatever score was rolled and assume this is a very special youngster, perhaps an abomination like Alia Atreides in Dune. So, for example, you could end up with a seven-year-old cleric with her wisdom well below 9. As a referee, be consistent about resolving this.
Cheating Methods: Everyone has their ways of altering ability scores. If this is customary, I'd suggest maxing one of the dice listed in the chart below (use some common sense here). So, for example, if a dice roll calls for something like d4+2d6, max out one of the d6s, so your score ranges from 3-16 to 8-16, with the average roll shifting from 9.5 to 12. I suggest this especially for prime requisite and Intelligence scores (to make sure that kid doesn't end up with the mental acuity of a squirrel).
Properly role-playing youngsters is more important than whatever statistical scheme. There is a lot to say about unsinkable childlike naiveté and the utter wonkiness of teenagers. It's all part of the game. How this all fits in my adventure, you'll find out at the end of this year when "How to Train your Wizard" comes out.
Age Groups
|
7-8
|
9-10
|
11-12
|
13-14
|
15-16
|
17+
|
Height us/m
|
49/125
|
53/136
|
57/146
|
63/160
|
67/171
|
69/175
|
Weight us/m
|
53/25
|
67/30
|
83/38
|
106/48
|
128/59
|
142/64
|
Strength & Constitution
|
d6+2
|
d8+2
|
3d4
|
d6+2d4
|
d4+2d6
|
Score: 3d6
Range: 3-18
Avr.: 10.5
|
Range
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3-8
|
3-10
|
3-12
|
3-14
|
3-16
| |
Average
|
5.5
|
6.5
|
7.5
|
8.5
|
9.5
| |
Dexterity & Intelligence
|
2d6+1
|
d6+2d4
|
4d4-1
|
d4+2d6
|
2d8+1
| |
Range
|
3-13
|
3-14
|
3-15
|
3-16
|
3-17
| |
Average
|
8
|
8.5
|
9
|
9.5
|
10
| |
Wisdom
|
d4+2
|
2d4+1
|
d4+d6+1
|
2d6+1
|
4d4-1
| |
Range
|
3-7
|
3-9
|
3-11
|
3-13
|
3-15
| |
Average
|
4.5
|
6
|
7
|
8
|
9
| |
Charisma
|
3d6
| |||||
Range
|
3-18
| |||||
Average
|
10.5
| |||||
Game on!
Edit: I forgot something I wanted to bring up. It's the old standard of giving XP bonuses to heroes with unusually high prime requisite stats. I suggest inverting the process. Anyone with prime requisite scores of 6-8 should receive a +5% XP bonus. With prime requisite scores of 3-5, the XP bonus should be +10%. Kids are like sponges. They learn fast!