I am considering some proxy tots myself, the 'real' ones look like cupy dolls to me. Reaper makes quite a few packs of assorted familiars, many of which look like imps and quasits, like this on:
http://www.ebay.com/itm/3578-A-FEMALE-IMP-Reaper-Bits-Animal-Familiars-/330746608603?_trksid=p4340.m1850&_trkparms=aid%3D222002%26algo%3DSIC.FIT%26ao%3D1%26asc%3D11%26meid%3D708933176410934409%26pid%3D100011%26prg%3D1005%26rk%3D1%26
As for young nephs, you might consider some of Reaper's succubi (especially Sophie, their mascot) they are obviously meant to be adults, but they fit the theme i think you are going for. Not a great fit, but doable.
Freebooter Miniatures also makes some femal demon figures that might work for mature nephalim:
http://www.coolminiornot.com/shop/miniatures/freebooter-miniatures/54mm-chaos-demoness.html
and there is also a freebooter succubus:
http://www.coolminiornot.com/shop/miniatures/freebooter-miniatures/succubus.html