It is one of the more painful versions of bedwetting for a family, and parents rarely say it out loud. A nine year old still wakes up wet most nights. Her six year old brother has been dry for a year.
Nobody planned it, and nobody says anything unkind. But everyone in the house can count.
It says nothing about effort
Nighttime dryness depends on two things a child cannot control: how far the signaling between bladder and brain has matured, and what the child inherited. Birth order plays no part. Neither does trying harder.
So a younger sibling who is dry first is not evidence that the older one is careless or not trying. It is evidence that two children, even from the same parents, run on different clocks. Bedwetting runs strongly in families, but it does not land evenly on every child in them.
The older child has already done the math
Parents often assume that if they don't mention the comparison, the child won't make it. She has made it. Children keep score of who can do what, and being overtaken by a younger sibling at something that feels babyish lands hard.
That is why it helps to say something first, before she has to raise it. Keep it short: bodies learn to stay dry at night at different ages, it has nothing to do with how good or how hardworking you are, and your brother's body just got there earlier. If a parent was a late one too, say so. Hearing that Mom or Dad went through the same thing does more than any explanation.
Don't celebrate the younger one's dry nights in front of her
When a small child stops wetting, the instinct is to make a fuss. Resist it, at least within earshot of the older sibling. Staying dry at that age is not an achievement the younger child earned. It is timing. Praising it publicly turns it into a competition the older child loses every morning.
Teasing is a house rule, not a punishment
Siblings tease, and most of it is survivable. This kind isn't.
The line should be simple and absolute: in this house, nobody comments on anyone's bed. Not as a punishment for the sibling who slipped, which only breeds resentment, but as a rule that protects everyone, the same way you would never allow jokes about someone's body. Stated calmly and enforced every time, it usually only needs enforcing a few times.
Keep the dry sibling out of the treatment
If the older child starts treatment, the younger one does not need a role in it. No briefings, no progress reports, no helping. The fewer people watching, the more the treatment belongs to the child doing it, and the better her confidence holds up along the way.
If they share a room, the practical side can be handled without turning the sibling into an audience. We have written about managing the alarm when siblings share a room.
What we tell parents
A younger sibling being dry first changes nothing medically. It changes a great deal emotionally, mostly for the older child, and mostly in silence. Name it before she has to, keep it off the family scoreboard, and if she is old enough to want this to stop, take that seriously.