Sorry bit manic at work so shorter than I meant to be. DD is 8.
Sticking to unprocessed as much as poss has seemed to help. But we do still allow some treats (including bedtime snack).
Setting a routine for bedtime - including relaxing together, drink of milk (sometimes warm, not a hot choc fan) and a snack (we do allow a cookie or a mini caramel slice for this to encourage eating it without delaying and having some food to avoid the "I'm hungry"'s), bathroom and pjs (calmly and quietly), then either a story or a few minutes of a quiet activity together (like colouring in once in bed, or giving her a sudoku, maths problems, word mining, word search or other mental activity sheets) could help to distract her brain and allow her body start to relax for sleep.
Dimming lights, playing music (gentle rather than boppy) or audio (audio books - DH has always had to go to sleep listening to R4 since about 10 yrs old and we are about to introduce DD to that).
Badger balm on wrists, lavendar oil or Neal's Yard aromatherapy roll-on oil for sleep over wrists, teetha granules (chamomile - she isn't a fan of Ch tea but happily takes granules) are all helpful for getting to sleep (not all at once though). If having a bath, sometimes we'd use lavendar or other relaxing types of aromatherapy bubbles, and DD also has a lavendar shower gel for shower nights. (Dozol has been used too on occasion, usually when we have either a cold or pain so the antihistamine or pain relief part are needed as much as the doziness part).
DD does now take concerta, and also has melatonin to help her sleep. THat suits us and we noticed a big difference (we are dealing with more than 1 Dx, so needed help in one area before we could tackle others).
DD does a lot of exercise (swimming, GAA, hiphop dance, athletics) and exercise days, especially later in the afternoon, do seem somewhat more relaxed in the evenings. Cycling to school or walking, rather than going by car (so she gets rid of some excesses first thing).
Only giving her a choice of 2 things (max of 3) rather than open-ended options to think herself and decide between loads is much better too.
While we haven't had to introduce them in school, my Bro's fiance (trained teacher) has said that often giving things to distract while getting them to concentrate can help. So she'd give some kids an exercise ball (stress ball) to squeeze with one hand while doing writing or something else with the other hand. Or put some kids sitting on "wobble chairs" (I believe it's a specific type of chair) or small exercise balls (yoga balls) while sitting at their desks working helped a good few (the "hyper" went into keeping them sitting when off-balance and they were able to concentrate on work rather than constant "jiggering" in their ordinary seat).
As there are 2 of them, is there anything you can give them to do with (or against) each other rather than trashing everything around them? Can you "release" them into the park to, say, follow a matching obstacle course with 2 footballs around cones or trees (or even plant pots in the back garden)? Are there any yoga or martial arts type classes they could do locally? (Helping to learn about controlling movement as well as actually doing lots).
And would either of them concentrate on "quieter" activities at any stage, like lego-building or computer games (there are plenty of educational types available). Set them competitions to see who can colour in the most sheets of paper (can be wildly enthusiastic about it) or build the highest tower with playing cards or lego or loo roll inners...
Oh, I just remembered, we also had a sand pit when DD was that age, and she used to love going into it and digging loads, making castles etc - but it all HAD to stay in the hippo pit or it would be got rid of. It was a handy thing to get rid of excess energy some days. And we are looking at getting a small trampoline for our tiny garden.