Sure? At least that´s not the case with the HRE, or I´ll have to check again.
However, if a faction leader had no adult male child, but an underaged son, once the son comes of age he still won´t be the heir, the previous heir will be the next Emperor (unless he dies sooner than the current Emperor, that is). Is that so only for the HRE or does it hold true for other factions as well?