Inside: The Nap That Never Happens: Auditing a Child’s Room for Light and Heat. Collaborative post.
Night sleep and daytime sleep are not the same problem, and treating them as one is why so much nap troubleshooting goes nowhere.
At night you are working with a room that is already dark. At one in the afternoon you are asking a child to sleep in a room lit by the whole sky, often at the warmest point of the day, with the rest of the house audible through the door. The routine is usually fine. The room is doing the sabotage.
Assess the room at nap time, in nap conditions
Close the door, draw whatever you normally draw, and sit on the floor for two minutes until your eyes adjust.
You will notice things you cannot see from the doorway. The band of light above the curtain pole. The brightness bouncing off a white wardrobe. The warm patch where the sun has been on the carpet since eleven. None of that shows up in a five second check with the landing light on.
Rank what you find by how bright or how warm it is, not by how easy it looks to fix. The easy fixes are usually the ones that made no difference last time.
Why clip-in blinds change the maths in a nursery
The obvious answer to daytime light is a blind inside the window recess rather than fabric hanging in front of it. The obstacle, in most modern homes, is that the recess is a sealed double glazed unit you should not be drilling into, and in a rented flat you may not be allowed to drill at all.
A honeycomb blackout blind that clips into the frame solves both at once. The brackets grip the frame or the beading instead of going through it, so the blind sits exactly where it needs to be, and it comes off again without leaving a mark. For anyone who has moved twice with a toddler, that second point is not a small thing.
The cell construction does the light blocking through its own thickness, and holds a pocket of air against the glass while it does it. That matters more at nap time than at night, because the afternoon problem is usually half heat.
Temperature is the half people skip
A room that is comfortable at seven in the evening can be several degrees warmer at two in the afternoon, and a warm child wakes early from a nap almost every time.
Feel the glass. Feel the wall. If the window is noticeably hotter, the sun is loading heat into the room faster than the room can shed it, and the only place to intervene is the window itself. Insulating the glazing does more for an afternoon nap than any adjustment to bedtime.
West facing rooms are the worst for this, and they are also the rooms where parents most often blame the routine.
Keep some rooms adjustable
One caution. Do not black out every room in the house. A child who only ever sleeps in total darkness travels badly, and a playroom or a living room that has been made dim at two in the afternoon is a miserable place to spend a wet Tuesday.
Use full blackout where sleep happens and something you can adjust elsewhere. The day and night blind range is built for exactly that middle ground, with sheer and solid fabric bands you can slide past each other to take the glare off without switching the daylight off.
Change one thing, then wait
The temptation with a failing nap is to change four things in a week. Do the opposite.
Fix the window, keep everything else identical, and give it ten days. If naps improve, you have your answer cheaply. If they do not, you have eliminated the most likely cause and you can look at the next one with a clear head. For the wider options, the blackout blind range covers the fabric and fitting choices in one place.