How it’s done
A sturdy notebook that travels in the child's backpack between one home and the other. Inside goes whatever he wants to put in from each world: the drawing of the week, the movie ticket, the new joke, the photo of the cake that came out wrong.
Rules for the adults, and they're strict: the notebook belongs to the child (parents write only if he invites them), it is never used as a channel for messages between adults, and it is never read as a file on what happens in the other house. It's the child's bridge to himself — not a diplomatic line between parents.
The 15-minute version: on arriving from the other house, a quiet while to «catch the notebook up» on whatever he wants to tell.
What it builds — the why
Continuity. For a child with two homes, the silent risk is living in two halves that don't speak to each other; an object of their own that crosses the border with them confirms that their life is a single story. Along the way: writing and drawing with real purpose, and a gentle thermometer of how they're doing — without interrogating them.
How it changes with age
3–5 Early childhood
6–9 Childhood
10–12 Preteens
What to watch for in your child
If the notebook always comes back full from one house and always empty from the other, it's not evidence to litigate — it's an invitation to look calmly at what rhythm the child has in each place. And if one day they don't want to show it, perfect: having secrets of their own is a sign the notebook is truly theirs.