How to get kids to actually sleep longer, not just stay in bed

[Firstaidnovice]

My DC (4 and 2) have always been early risers. We've tried everything, or so it feels. Thing is, I don't even really mind early mornings so much, because I can just have early nights myself, but they are so bloody tired all the time! On rare days where they actually sleep past half six our days are so much happier. The difference in the levels of whining for instance is remarkable.
Anyway, through many reward charts and bribery they both generally stay in their rooms until 6.30, with the aid of gro clocks. But the eye rubbing, yawning and general grumpiness tells me they are awake much earlier, and just waiting.

So, my question is - is there anything I can do to encourage better sleep? Or help them learn how to actually go back to sleep when they wake early?

Their rooms are totally blacked out by the way. Double black out blinds. Youngest also has white noise. I've tried wake to sleep more recently but youngest is such a light sleeper I ended up waking him for the day at 4am a few times, which was obviously a nightmare.

I'm pretty sure the answer is to just wait until they are older, but I'm willing to try anything!

I feel your pain as DD1 is hard wired with a 5am wake up!

I think you're on the right track wanting to encourage them to sleep rather than rewarding them to stay in bed. With DD1 I used to go in her room, say "it's still sleepy time" and offer to stay next to her cot while she went back to sleep and I would sleep on the floor for an hour or so. If she was really intent on getting up we would do but I would try and keep everything low key, e.g. Reading in her room with dim lights.

She still stirs and wakes at 5am but now gets herself back to sleep until 6:30 (she's just over 2 now).

I can sympathise as it's so frustrating when they insist on getting up but then spend the whole time rubbing their eyes and yawning!

What time is bedtime and how do they go to sleep in the evening?

Are either having daytime naps? What time and where?

If either wakes in the night, how do they go back to sleep?

Bedtime is officially 7, but more often 6.30 as they are so tired.
They go to bed after a few stories and songs, but fall asleep by themselves.
If they wake in the night they just go back to sleep by themselves, sometimes a quick cuddle and song. Unless it's after 4, which is when they are unlikely to go back down.
4 year old at school, so no nap. 2 year old doesn't routinely nap, but sometimes has one if he's been up really early.