User blog comment:Noyas/Some questions about bleach./@comment-44061-20100425015351

Children can be borne is Soul Society, hence the families there.

As for who fill the spots most people tend to speculate though In truth they have no idea. The reality of the situation is that it takes more then simply having bankai to be a captain. Thats what the criteria is for becoming one without a doubt but Renji has alot to learn about his own bankai as well as being in that position. Ikkaku doesn't even want the position and although Urahara and Yoruichi are currently exiled (Urahara officially) that very well maybe lifted in light of the events being revealed. Some unknown Shinigami may achieve the status of captains well over the lieutenants everyone speculate will get the positions, as that tends to happen in military advancement. Sometimes is a completely new outsider. Ichigo is less eligible then anyone.