silkies are not teh best of layers, but will make lovely pets for your daughter.
i don't know about keeping them with australorps, but they are best not kept with birds such as isa browns, who will pick on them with their gentler natures.
is it possible to make a pen in two parts, or maybe, get some isabrowns that are only babies and they can grow up with the silkies as the bosses, and this usually extends into adulthood.
its a tough one, cuteness vs egg productivity.
on the plus side, i have found silkies to be good winter layers, but they don't tend to lay much at other times of the year.
Anconas, Silkies and Pekins Caladenia CottageSilkiesWonderful Silkies