The child template is considered appropriate for creatures below the age of adult for that race. The abilities here are adapted from the ability modifiers for children in d20 Modern.
"Child" is a template that can be added to most aberration, animal, fey, giant, humanoid, magical beast, monstrous humanoid, ooze, outsider plant or vermin.
Individual creatures may be inappropriate for the child template; many giants have specific statistics for children, while some outsiders or aberrations may not have children at all.
While undead are generally not appropriate for the child template, the zombie, skeleton or vampire templates may be added onto children, though good taste may or may not forbid this.
Size and Type: The creature's type remains unchanged and does not gain the augmented subtype. It does gain the "child" subtype. Size is reduced by one category.
Hit Dice: Hit dice are halved, rounding down. In many PC races (human, elf, dwarf) as well as other creatures of 1 HD or less, this may result in fractional hit dice; see below for standard rules concerning creatures of fractional hit dice.
Speed: The base creature's speed is halved, rounding down. Unusual speed modifiers (the Dash feat, the expeditious retreat spell, caltrops, etc.) are handled normally for the new speed.
Armour Class: The creature's natural armour is reduced by 1 (minimum 0). Remember to adjust AC for the new size.
Base Attack: A child has a base attack appropriate for its new hit dice total.
Attacks: Children are weak, but not helpless - especially children of powerful creatures. A child retains all the attacks of its base creature. Remember to adjust natural attack damage for the new size.
Damage: Normal, as adjusted for the creature's size.
Special Attacks: A child retains all of the base creature's special attacks. Remember to adjust level-based benefits for the new HD value.
Special Qualities: A child retains most of the special qualities of the base creature. Its damage reduction is reduced by 5 (minimum 0).
Saves: A child has normal saves for its hit dice.
Abilities: The base creature's strength and constitution scores are decreased by 3. Its dexterity, intelligence, wisdom and charisma scores are reduced by 1. If the base creature's size has been reduced (all creatures except those of Fine size by default), reduce strength by a further -2 for a total of -5. Remember that creatures of an intelligence of 2, 1 or - default to that number despite such adjustments.
Skills: Racial modifiers are unchanged. A child's skills are adjusted for its new HD and intelligence score.
Feats: A child's feats are adjusted for its new hit dice value. Remember to adjust feats the child no longer achieves the prerequisites for (due to changes in HD, abilities, etc.).
In addition, a child does not receive bonus racial feats (human's bonus feat, elven weapon proficiencies, kuo-toa's Alertness) as long as it retains the child subtype.
Environment: As base creature.
Organization: Creatures of an intelligence of 2 or higher usually stay with their parents, while creatures of an intelligence of 1 or less are usually left for themselves or with other children.
Challenge Rating: As base creature -3.
Treasure: Usually none.
Alignment: Often neutral. Children's minds are still growing and are generally more plastic than adults, though more extreme alignments are not unknown.
Advancement: Special, see text.
Level adjustment: N/A; see text.
Advancement: Children do not gain hit dice with experience and cannot be advanced. A child's only way to progress is achieve adulthood. Adulthood occurs at a set age (15 for humans; other races vary wildly), though highly unusual magical or genetic effects may cause a creature to reach adulthood sooner or later.
Once an adult, the child loses the child subtype and all the effects of this template. Its hit dice return to normal and its reduced or disabled abilities are restored.
Level adjustment: Children are inappropriate for player characters due to their inability to advance in levels. If for some reason, a PC wants to play as a child prodigy, the character should be treated mechanically as an adult. Due to the highly unusual nature of the situation, any adjustments to ability scores, size, speed or other factors should be carefully judged by the DM on a case-by-case basis.
The following fractional HD rules are extrapolated from fractional HD animals in the Monster Manual. Though care is taken to assume accuracy, viewers should not take this information as verbatim official rules.
Fractional HD reduce the hit points of a creature by the value of the fraction. For example, the normal value of a d8 is 4 (rounding down); the hp of half a d8 HD would be 2, while a quarter would be 1, etc. Meanwhile, the normal value of a d12 is 6, making half a d12 HD equal to 3 HP and a third of a d12 HD equal to 2 HP. Fractional HD appear to be treated identically to a single HD in regards to skill points, base attack and saves (four times normal skill points in a level, +1 or +0 BAB, and good saves +2/bad saves +0).
Fractional HD in an intelligent race which progresses by character class are much more theoretical, as 3.5 appears to retain no such examples (as compared to the fractional HD kobolds of 3.0). They are assumed to act identically to the rules above. It can be assumed that fractional class HD have no class features (such as barbarian rage, spells, or bonus feats), making a ½HD wizard unable to cast spells and a ½HD paladin unable to smite evil.