Oh gee, TV and devices (phones, tablets, etc) are really, really stimulating for all brains, but particularly small brains. Each kid is different, but a routine is essential for most kids - it established a predictable, reassuring pattern of behaviour (note that a routine is not necessarily a schedule - it's 6:35pm, so we must do this, etc - but a predictable sequence of events). My kid at 12 needs a routine, and thrives on it. She can become quite concerned when the routine is broken, but that gives us the opportunity to reassure her that some deviations are OK, and learn to cope with them (she used to get worried if we didn't drive the usual way to a known destination).
Thinking about last night - husband cut his finger at about 5:45pm, we went to northside emergency to get it seen to. His parents are over for dinner (and babysitting, as we were meant to see a play at QPAC at 7:30). We get home some time after 9pm. ILs are sitting downstairs watching TV (having finished the dinner making, feed the child and themselves, etc). My MIL comments that she thinks Not So Little Miss is probably asleep.
I go upstairs - Not So Little Miss is wide awake and hasn't even showered yet. She still needs to be reminded to do these things, as she gets distracted. She doesn't automatically follow the regular night-time routine without some prompts. My ILs seem to think she's so grown up, and fair enough, everyone was a bit distracted with the night's excitement … but even a 12yo can need to be told to go to bed! (Given her Dad had been to hospital, I wasn't surprised that she was awake, just surprised the evening routine stopped at dessert, and the ILs just assumed she was doing the right thing). 8pm is when we try to get her into bed (8:15 is more realistic), and it's light's out at about 8:30 after some reading.
The dessert > shower > into bed and red > lights out sequence is important for my girl, and if we skip the reading in particular, her brain doesn't calm down as much, and she won't fall asleep quickly. She also can rarely admit that she's tired - it's like accusing her of committing murder!!