you could try Willowbrook in Gingin - was lovely place - no beach but stuff to do nearby.
they use to serve scones jam and cream on a Sunday morning to all the campers for free.
Only thing was the shower block was a demountable one so was flooded with water and there was a shared kitchen facilities.
But knowing that now (and if its still like that) I would be better prepared.
Stayed at Mandurah caravan park and that was fantastic as the camp sites were around the playground area.
My favourite place is a bit further away so maybe for another time. Taunton Farm Cowaramup
(near Margaret River) best family camping place ever !