My son is 2.5 and suspected ASD. He hasn't slept more than 4.5 hours broken sleep a night for about 4 or 5 months, it nearly ended my marriage as we were so exhausted and has caused many a sick day at work (I'm a nurse and do 12.5 hr shifts).
Anyway we finally started melatonin last night, he went to sleep at 7pm (literally never happened) and woke only once for 20 mins overnight, and woke for the day at 7.35am. We haven't slept till 7.35 since my eldest was born 3.5 years ago! We were nearly late for work because we never set an alarm now as we wake every day at 5am with him.
Tonight he was crying to go to bed at 6.45! Please tell me this will carry on forever 
I can't tell you the relief I am feeling at the moment! I had to share here as I know you lovely folk will get this!