God assigns souls to children based on overlapping criteria of what kind of kids the parents deserve, and what kind of parents the kids deserve (as well as all the other factors in His Judgement that aren't typical of every situation). This doesn't necessarily mean balance (bad kids need good parents, and bad parents need good kids), but it does mean reward/punishment. Once you get to a certain stage of embodying Deen, then you're almost guaranteed to churn out perfect kids. An incredible majority of the higher level spiritual guides or ulema I know of have had children who turned out IDENTICAL to them in religious/spiritual respects, while of course remaining completely individual.
Mufti Muhammad Shafi (Ma'ariful Qur'an)... his son is Mufti Taqi Usmani (who later revised that and supervised the English version). That's just enough said right there, that his son reached the same ultimate stage of scholarship. Here's the dedication to a book he wrote, "An approach to the Qur'anic Sciences".
"To my respected father/ Maulana Mufti Muhammad Shafi (ra)/ in whose person lay for me/ the compassion of an exemplary - nay, an unmatched father, an impeccable teacher, and a sagacious guardian and mentor./ and to none else on earth/ my love and my devotion are directed./ My Allah shower Mercy on him./ Without his prior permission do I dedicate this little effort to him with the submission./ [some urdu]"
-Justice Mufti Taqi Usmani (Ret.)
Another popular instance, Hazrat Umar Ibn Khattab (RA), his son was Abdullah Ibn Umar (RA)... who was actually as qualified for the Caliphate as even other Sahabah. :0! Umar didn't want to turn it into a dynasty, so it went to Uthman (RA) next.
Yet for normal people, we're to expect to turn out kids that are probably nothing like us in terms of 'soul' but just like us in outwards ways (appearance, personality, etc.). Yet these people brought up children who had similar souls (the good kind) but their true individuality showed through in that they were hardly anything like their parents. The one true measure of a person (Deen) was what they had in common with their parents. It's amazing how something like faith can be a factor in turning out the genetically perfect combinations of genes (diversity in offspring).
And yet for so many 'religious' people now (the ones closer to 'our level', the ones we're likely to know personally), they wind up with kids that are the opposite of them in terms of kindred souls but physical/mental clones otherwise. Sincerity in religion it seems, is not a common thing amongst the people. Or maybe sincerity is not enough and you just need to be THAT damn good.
It's highlarious how people nowadays talk about giving their children their 'space', to let them 'find themselves', etc. etc. Only to wind up with the kids being clones (for better or worse, usually worse, even if it appears better at first sight) of themselves. It's like the metaphor about the painting. Silly people, simply dabbing at a canvas with a brush in the imitation of a great painter is pointless if you don't have the right paint on the brush, or the right order and placement of the brushstrokes. You think you're being enlightened parents, but there's no end result.
As I said earlier, if a child can ask over 400 questions a day, you should be able to explain Allah in 400 different ways a day.