D is 17 months and has never really slept through. He will always waken up once which I used to deal with by cuddling or shushing back to sleep... Sometimes for up to an hour, he would then get up for the day at 5ish.
However, I'm now my 3rd trimester of a twin pregnancy and find our routine too difficult so I've been bringing him in with me and H moves to the spare bed. When he's close to me D will sleep until 6, 7 or sometimes 8 and I feel much better.
I know it's not ideal and I've had all the 'rod for your own back' comments but frankly I'd rather get some sleep than follow the supposed 'rules'.