Sleep, sweet sleep...
Anyway. Two quick things that will have further explication, once the rest of the notes can be put down from their current, rough form.
First, alternate basic character generation in GPS will be handled in the GPS Master Guide. This will specifically reflect the tone of the campaign. If it is a Gritty-level game, it will be something along the lines of a 3d6 Organic, where the Tactical Game will allow 4d6, drop the lowest die. Action will allow 4d6, drop the lowest die and re-roll any 1's rolled. Cinematic will be 4d6, drop the lowest die and roll six sets of stats to pick the best single stat group from.
Second, GPS Children (either a sub-game or a useful guide for flashbacks and the like) will work with the following:
If generating characters at a basic level, the stat generation will be 2d6+1 (Organic, at Gritty), 3d6+1, drop the lowest die (at the other levels, with the logical modifications). This will generate a 1st level child's scores. From here, the character has 10 levels to advance through before they are able to take an adult character class. Every 2nd level (2, 4, 6, etc.), all of the character's attributes will advance by 1, ending with a +5 to all stats at level 10. This is adjusted downward from Cinematic (giving a range of 8 to 18 for Stats) to Gritty, where the characters would advance three separate stats by 1, every second level. (Cinematic - 6/6, Action 5/6, Tactical 4/6, Gritty 3/6, Surreal random)
Skills would advance accordingly. At 1st level, the character would get a set number of skill points, adjusted by Intelligence. This would be a single rank in a skill. At 4th, 7th and 10th levels, the character would gain a point for their Trained bonus in that skill, so that at 10th level, they would have a full skill according to first level character in a regular game. In a Gritty game, this would be all the skills they would be able to have. In the other Genre systems, they would be able to gain other skills, which would automatically raise as well. (No skill would be able to raise above 1 rank, but if a new skill is taken at 4th level, it would have 1 rank and 1 trained. At 7th, 1 rank and 2 trained, etc.)
Each level would represent a year's time. Assuming that a minimal age to start a character in a GPS Children game would be 9 years old (a 4rd grader, give or take), this would advance the character to age 18, by the time the character progression finished. (Much of this is up to particular GM flavor, but at the moment, it's a rough guideline. It might be a better plan to start at 14 years old and advance each level every 6 months, depending on the particular game.)
This can be used in a number of ways. One way would be simply to use it as means to pull a character into a subrealm where they have to play as their juvenile selves. In doing so, they would have to face childhood fears, deal with being powerless, or whatever the game required. Alternately, this mechanism could be used as a campaign base, where the characters must deal with something as children that forms the background of their eventual adult characters. (Stephen King's It is an immediate example where the sections as children would work as a necessary prelude to the characters as adults.)
Finally, the specific genre informs a lot of the base for the game. As children in a Gritty game, they would likely be the victims of child abuse, as that would be realistic conflict that would affect them as adults. In a more Action or Cinematic game, they would be Boy Adventurers like Johnny or Rusty, the Hardy Boys, Nancy Drew, etc. Also, this would cover how damage would be covered. Action and Cinematic would have the characters captured when knocked out. Gritty would be scarifying and deadly.