So stop putting them to bed so early.
If you look at the brain with the entropy model that we’ve proven, kids have the lowest amount of brain entropy [in general]. Because they have the lowest amount of brain entropy, they need less recovery time to zero out the stresses of their day. Read my post about sleep for more on how this works.
It’s why you can’t keep up with them. And Coffee is not going to help you, long term.
It’s why they have so much energy. Science has shown that they have greater energy levels than endurance athletes.
There is no set amount of time that anyone should sleep. Especially kids. What’s important is that they enjoy their days enough to not want to sleep, and that they can identify when they start getting tired and lay down.