I took your quiz, and opted for maximum user input, however:
All of these things should be bound together, I think.
The soveriegn controlling the father of the child should get control of the child... TO BEGIN WITH.
He should then be presented with options in certain years (turns) as the child ages.
These choices can effect the outcome of the child's future, however, each choice should have a chance of failing. The more powerful the bonuses each choice gives, the higher the chance the training will fail. At the end of the child's development, there should be a roll based on how many times the child failed in his training. If he passes the roll, he continues to faithfully serve his father. If he fails it, he either 'rebels' to his mother's faction, or rebels altogether and joins an enemy faction, depending on how harshly he has been used. This would be the most fair, reasonable, and interesting to the player system.
It makes daughters less valuable than sons, as you are unlikely to control their offspring, but still valuable as diplomatic tools, which is highly authentic to a medaeval/fantasy mindset. It also allows the player to attempt to control the outcome of their progeny's fate, but does not guarantee success.
It should also be an option to 'do nothing', at each career choice, which should have the effect of giving the child a random talent, skewed towards laziness and worthlessness, but no chance of rebellion.
This system gives the player the choice of gambling on a difficult training schedule that COULD produce an ideal hero, but may 'break' his child's spirit, causing him to defect later, or to take a safer route and be content with a less stellar progeny, but one who will almost certainly serve. This seems fair, 'realistic', and satisfying.
What do you all think of this system?