The Innaminkah destination sounds pretty good as there is a bit to see apart from WA and those across the top, it would be a good three day hard slog to get there, SA would come in by Walkers Crossing , Southern QLD VIC and NSW mainly would come via Tibooburra , Northern QLD through Cordillo Downs.
Coongie lakes would be a great spot , has a camping area, depends really on numbers, I dont think the area lends itself to great numbers being there all at one time, I would seem to think it would be a day out and stay overnight and back the next day from Innaminka .
To me unless you are seasoned traveller in these parts, travelling in these parts with a handbrake and kids is going to be a forgettable experience for them .
I would certainly start thinking in terms of a destination that is ease of travelling to for famillies and not something that is Geographically central . I would recommend something in the North East Victoria South Eastern NSW would be something more appropiate , I once suggested Tom Groggin, Davies High Plains area, not because it is relative close to Victoria and NSW but because even from Adelaide or Brisbane is a comfortable 2 day trip even for old farts and there is plenty of High country to see .
I know I will get yelled down in flames but just for a moment consider who we are going to try and attract to what we enjoy .
My two bobs worth .
Simmo