That and prestige loss from children not having their own lands needs to be removed. It's unfair to be a 1 province count in the HRE and through no fault of your own have like 7 sons or something from your wife. You're poor, you'll never gain land in any significant time, and once they all become of age your prestige is going to tank big time.
Taken into account the spirit of CK, maybe there should be also something like "
bloodline score" in the game, measuring the ruler's ability to manage his dynasty, and the "quality" of it? This score could be reflected in the monthly prestige change.
Currently marrying your daughter gives you onetime prestige bonus; and adult sons without a land, and unmarried daughters cause a prestige diminish every month. That's pretty much it.
But when assessing success of dynasty and reflecting it in prestige, why not to do it on broader bases?
For example, some basic factors that the hypothetical "bloodline score" could take into account might be:
* number of sons, children, and grandchildren;
* some weighted average of ruler's, and his childrens', and grandchildrens' character stats (martial, diplomacy etc);
* per cent of children and grandchildren having "diseases traits" (especially inbred, maniac, and schizophrenia);
* social positions the children and grandchildren have (in feudal system (kings/dukes), and in courts (advisors));
* social positions of husbands of married daughters;
* claims on titles that ruler, his children, and grandchildren have;
* some weighted average of parents' and grandparents' "bloodline score" (with a fade factor).
This score would capture some important indicators of dynastical success, and compress this broader picture into one figure (which would in turn become one of the factors that influence monthly change of prestige). And it would deepen one of the main strengths of CK - the human, and role-play component - even further.
(In that way, for example, the penalty of having sons without a land is somewhat relieved by the effect having sons at all. Etc.)