I am a DM that gets pretty heavy into the science of the game so when I am asked a question I like to back it up with as much rules and facts as I can. This particular question is reguarding the rules behind PCs having children. How do we determin the child’s ability scores? What if two PCs have a child? Are there rules for this??? Do the PCs high stats effect the stats of the child?
Woot! You know you've had a healthy campaign when it goes long enough that pregnancies and offspring are a legitimate issue.
Back in my 1e days when this first happened, I created complex rules around determining the children's attributes and personalities based on a combination of genetics (attributes and alignment of the parents), destiny (level of the parents), and astrology (when the kid was born).
Basically, attributes are rolled randomly from dice pools. For each 6 points of the combined ability score of both parents, you get one dice. So if the parents strength sums to 24, the kid gets 4 dice (take the best three) to determine strength. If the parents both have 18's in intelligence, the kid gets 6 dice (take the best three) to determine intelligence. You get 1 bonus dice in all attributes for each parent that is at least a 5th level character, and 2 bonus dice for each parent that is at least a 10th level character - provided that the parents offer appropriate sacrifices in honor of their child's birth and properly conduct all rituals around the child's naming. These represent the blessings of the gods, fairy god mothers, ancestors and other concerned parties.
This will tend to generate children with rather high ability scores if the PC's marry well. Heroes begat heroes (or villains, depending on the personality).
Alignment was determined randomly from a table, with the entries being things like 'alignment of father', 'alignment of mother', 'one step more lawful than father (or same if already lawful)', 'one step more evil than mother (or same if already evil)', 'two steps more good than father...', and so forth. The most common results obviously would favor the child inheriting the parents predispositions.
Personality and to a small extent attributes were further modified by the zodiac and by the planet the child was born under (zodiac following the calendar, and planet being determined randomly). Personality was determined by slightly modifying the tables for randomly determining NPC alignment in the 1e DMG - reorganizing them so that linear modifiers made more sense. Each sign or planet gave modifiers to the rolls. Ability scores had a small chance of going up or down depending on the sign born under (Leo for example gave something like a 10% chance of +1 strength, a 10% chance of +1 charisma, and 10% chance of -1 wisdom. Cancer on the other hand gave mostly negatives, but boosted the chance of naturally occurring psionics under the 1e appendix rules.)
Modified for 3e, I'd probably have rules for determining the 'Traits' of the child.
Of course, these represent the adult stats of the character. There were also rules for determining the stats of the character at any age given the stats of the mature character, as well as rules for children acquiring XP from training and education. So, you get to know just how dangerous your 9 year old is or isn't.