I’m very strict with our kids’ bedtimes and for both of them, I have established night time routines pretty much from the day they were born.
With Molly it was: bath, pajamas, milk, lullaby, sleep.
With Benny it is: pajamas, milk, asking Molly not to turn the light on, telling Molly to turn the light back off, holding Benny in the dark room silently while attentively listening to the noises from the lounge and hoping he’ll fall asleep before Molly gets bored of watching TV.