For ages, DS2 has slept for about an hour in the afternoon, and 11 or so hours at night.
He seems to suddenly only need 11 hours total, so is waking up really early in the morning.
I can't work out what's waking him, but I can't believe he doesn't really need more sleep. (Not least because he's tantrumming lots.)
He has a noise machine ... I guess I should try checking his blackout, because it's a bit makeshift. (Am meant to be installing proper blinds in there, actually ... maybe should do that ...).
DS1 is 5, and seems to be sleeping more than DS2 at the moment ...