MrsMSP and I just returned from a Great Ocean Road bus tour booked via viator dot com that I can only describe as a "can't miss" ^^^ - the tour company was called AATKings. Great information, history etc was provided and I'm sure you're kids will marvel at the scenery. Both my wife and I concluded it was one of our top 5 travel experiences ever, and we've have traveled extensively.
You could look into staying at Port Campbell. Its torward the "end" of the great ocean road near the London Bridge - very cute little town that has everything you need for a relaxing holiday. I do imagine they book up well in advance.
Cheers!