Kids holds each child's details in one place both parents can see: doctors and dentists, school and teachers, allergies and medication, clothing and shoe sizes, and documents.
Adding a child adds them for both parents. Updating a detail updates it for both — there's no version of this that only one home has.
Why it's worth filling in
The practical win is the small stuff. Shoe size, the dentist's number, which inhaler, the teacher's name. Things that are genuinely needed on a Saturday afternoon and that nobody wants to have to ask for.
Keep it factual. Children's information is part of the family record like everything else, and it isn't the place for opinions about the other parent.