I don’t have children, so this might not be useful, but things that have helped me are:
Proper “bedtime routine”. Each night I light a nice candle in the living room, and before bed I brush my teeth, turn out all the lights, then go in and blow out the candle. It’s like switching off the day.
Bedroom not used for anything except sleep and sex. No TV in there, no reading or phone/tablet in bed.
Earplugs - probably no use if you need to wake up for DD, but my partner is a terrible snorer - and complete darkness.
Magnesium supplement about 30 minutes before bed. You can also get it as a spray you apply to your skin.
Lavender oil - I rub it round my nose just before getting into bed. Also a pillow spray. The best one for me is the This Works Sleep Plus spray, but it is expenny.
If unable to sleep/get back to sleep I have several mental tricks. I count backwards from 100, go through the alphabet and name a thing for each letter (animals, countries, household appliances and so on. I never do the same thing twice in a row), go through class registers (no use if you are not a teacher!). The other thing that I sometimes do is imagine myself in a white room, like a spa, lying down in a robe, soothing music, nice smells - I use this to fall asleep - and try to visualise each thing and how relaxed it makes me feel.
I am a terrible worrier, so I do a to-do list for the next day after dinner. Writing stuff down really helps me switch off from it because I know there’s a plan. I use my phone, but went through a phase of keeping a notebook in my bedside table - I found if I woke up at 3am feeling anxious about something, writing it down and how I would deal with it kind of shut it off.
I also prefer to go to bed either before my partner, or after he is asleep. If we go together and cuddle/whatever or chat, it’s like my brain forgets I have gone to bed to sleep.
(Apologies if this all sounds like nonsense!)