If they are hungry, look at their diet - how they eat and what they eat. Try: cutting all sugar after 4pm, cutting processed foods after 4pm, reducing carbs and increasing protein and veg, which will all help stabilise blood sugar overnight and keep them fuller for longer. Make sure they have a substantial dinner. And make sure they understand they need to have a substantial dinner full of protein and veg, because they are waking up hungry, so what they are currently eating isn’t working. Maybe leave a banana next to their bed, so they eat that and go back to sleep if they are hungry before it’s time to get up.
They are used to waking up early now, so you will have to break the habit. Invent consequences rather than incentives, because at the moment, their whinging seems to be rewarded and they get what they want. Put a clock or groclock in there and set a rule that they must stay in bed until 8am - they are old enough to do that. If they can’t, you’ll be so tired during the following day and moaning about your own exhaustion, that you’ll have to cancel the lovely plans you had for them 😉 or delay / shorten them etc.
Make sure they know at bedtime (and through the day) that you need your sleep to keep your brain healthy and that the consequence of getting out of bed for no reason before 8am, is you will be too tired to have a lovely day - it’s an important lesson for them both about sleep, consequences and kindness. They need sleep to keep their brain healthy, as well as for good mental health. If they have the habit of staying in bed and there isn’t an incentive to get out of bed, then they might start sleeping longer as well.
Good luck - sleep is so important and setting healthy sleep habits for the kids and looking after your own sleep is protecting your health.