I went back through the marked-up copy of Plato I used during undergrad, but I unfortunately couldn't find any pithy quotes on the subject. It's in books V and VI, if you're interested in looking yourself.

Note, though, that it's only the Guardians and the Auxiliaries who don't raise their own children. The lower classes ("bronze" citizens) will have family units just like they always did.

(From Julie / eveglass -- I have no OpenID.)