The night you bring the baby home, your firstborn gets bigger. Not older. Bigger. Their feet are suddenly enormous on the stairs. Their voice, which was a normal voice yesterday, is now too loud near the bassinet. Their hands look rough. And at eight o'clock, the child who has gone to bed without fuss since they were four is standing in the hallway in pajamas asking for water, then for a different blanket, then for you to lie down with them, just for a minute, and you feel something you would never say out loud. You are annoyed at them for needing you.

Most parents know this feeling and almost none of them talk about it. So let's start there, because the bedtime problem that shows up after a new baby is really two problems braided together: the child's, and yours. Both have a cause, and the cause is not that your older child has become difficult.

The hour that got taken

Think about what bedtime was, before. For a four- or six-year-old, the last half hour of the day was the single most concentrated dose of undivided parent they got. No phone, no sibling, no dishes. One adult, one book, one warm body in the dark. Children do not count minutes, but they feel density, and bedtime was the densest part of their day.

Then a newborn arrives, and newborns are at their fussiest in the early evening. Cluster feeding, the long inconsolable stretch that nurses and exhausted parents call the witching hour, the baby who will only settle on a chest: all of it tends to peak between dinner and nine. The exact hour your older child most needs you is now the exact hour the baby most needs you. This is not a parenting failure. It is a scheduling collision built into the biology of two different ages.

Judy Dunn's classic observational studies of families in the weeks after a second birth found what parents already suspect: firstborns became clingier, more tearful, more likely to have trouble at night and more likely to be "naughty," and mothers, worn down, spent noticeably less time in play and conversation with them than before. The child lost something real. The regression is the receipt.

Why they act younger, not older

Here is the mechanism worth understanding. Attachment behaviour, the whole repertoire of clinging, calling out and needing to be close, is not a habit that gets trained in or out. It is a system that switches on when a child perceives a threat to their bond with a caregiver. A new baby, from the firstborn's point of view, is a plausible threat. They watch you answer the baby's cry instantly, every time. They watch the baby get held for hours. They are not stupid. They draw the obvious conclusion: being small gets you held.

So they get small. The baby talk, the wanting to be carried, the sudden inability to fall asleep alone that they had mastered a year ago. Psychologists have used the word regression for a century, but it is less a slide backwards than an experiment. The child is testing whether the old moves still work. And the cruel irony is that the more unpredictably we respond, sometimes giving the extra cuddle and sometimes snapping "you're a big kid now," the harder they push. Behaviour that is rewarded only now and then is the most stubborn kind there is.

This is also why the usual advice, to give your older child more attention, tends to fail. There is no more. You are running on four hours of sleep. What a child's attachment system actually responds to is not quantity but reliability: a piece of you they can count on at a known time, that does not depend on whether the baby is crying.

The thing on your side of the braid

Now the part nobody says. That jolt of irritation when your firstborn looms over the bassinet is partly perceptual contrast, the same trick that makes a grey square look dark on white and light on black. Your brain has been recalibrated by a seven-pound reference point, and against it a thirty-five-pound child looks like a giant. Their normal volume reads as loud. Their normal clumsiness reads as dangerous. You are seeing them through a newborn-shaped lens, and the lens distorts.

Knowing this does not make the feeling vanish, but it changes what you do with it. The child did not change. Your measuring stick did. If you can hold that thought for ten seconds in the hallway at eight o'clock, you will say something different from what you were about to say.

Brenda Volling's long-running research on firstborns adjusting to a sibling is reassuring on the big picture: most children either sail through or show a short bump in difficulty that fades over a few months, and the children who struggle longest tend to be those whose family relationships were already under strain. The adjustment is not fragile. It mostly asks for one thing: that the older child learns, through repetition, that there is still a corner of the day that belongs to them.

Make bedtime theirs, and make it baby-proof

The fix is not a longer bedtime. It is a bedtime with a guaranteed shape. Two features matter.

First, it has to be named and claimed. Not "big kid bedtime," which has quietly become a phrase that means "the one who gets less." Use their name. "This is Theo's bedtime. The baby isn't invited." Children between four and nine understand ownership with great precision, and a ritual that is explicitly theirs becomes something they protect instead of resist.

Second, it has to survive the baby. If the whole routine depends on you being free, it will break on the nights the baby cluster feeds, and those are exactly the nights your firstborn's alarm system is loudest. So split it. Most of the sequence, pajamas, teeth, choosing the book, starting the story, the breathing, the sounds, can be something they run themselves, with pride. What you provide is the bookends: a sentence at the start that promises you will come, and two minutes at the end where you actually do, even if the baby is on your shoulder when you do it. Two reliable minutes outperform twenty minutes you can only sometimes deliver.

And when the regression shows up, meet it once rather than correcting it. "You've wanted me closer at night since the baby came. That makes sense. I'm still yours." Putting a feeling into words does for a child what it does for the rest of us: it lowers the pressure to act the feeling out. The child who is told, kindly, what they are doing often stops needing to do it.

Your next moves

  • Tonight, make one promise with a time in it. "After the baby's feed I come for your story at 7:30, no matter what." Then keep it, even if all you can give is five minutes with a baby in a carrier. The time of day matters more than the length.
  • Hand them the first half of the routine. Write or draw the steps they can do alone: pajamas, teeth, pick the book, start the sounds. Let them tick each one off. Competence is the opposite of regression, and they get to feel it every night.
  • Retire the phrase "big kid" for a month. Say their name instead. "This is Ada's bedtime" lands as ownership. "You're the big one now" lands as demotion.
  • Name the regression once, warmly. Pick a calm moment, not the hallway standoff, and say: "You've been wanting me more at night since the baby came. That makes sense." Then say nothing else about it.
  • Tag-team for the first six weeks if you can. The parent who is not feeding takes the older child's bedtime, every night, so it is never the thing that gets cut when the baby won't settle. If you are solo, the baby rides along and the script stays identical.

A ritual that runs even when you can't

This is close to the reason Nightlamp exists. It is an eight-minute bedtime ritual for kids ages four to nine, one calming story, a short breathing sequence and a sleep-sound mix matched to their age, that a parent sets up once and the child runs on their own. On the nights the baby chooses 7:30 to fall apart, the older child still gets the same story, the same breathing, the same ending, and you still get to walk in for the two minutes that matter. If you'd like to see how it works, it's at https://nightlamp.lumenlabs.works.