The information I found online is inconclusive regarding the minimum age for independent applications for children. Does anyone have reliable information specifically for school age kids?
It depends on the canton.
The absolute minimum to fulfil the federal criteria is age 9 which would apply if a child was born here but some cantons have additional criteria so you need to check with the canton you’re applying to.
Asking specifically for Zurich.
In Zurich, children can apply for independent naturalisation through the simplified process under certain conditions:
They must apply before the age of 22.
They need to prove five years of residence in Switzerland, including three years immediately prior to the application.
For ordinary naturalisation, the minimum age is 9 years, provided they have lived in Switzerland for at least 10 years (time between ages 8–18 counts double).
Minors under 16 require a legal representative to apply, while those over 16 must also declare their intent in writing.
Our 3 kids each applied separately in different years at the age of 14, 12 and 9. I filled and signed their papers, as mother, but they were treated independently. The older two already got their passports, the youngest will likely get this summer. We, the parents, will reach the 10 year criteria only in a few months.
Older kids had to pass B1 language test since they spent a lot of time at rhe international school. The youngest was excused from language requirements, since Delf Junoir B1 is only offered from 12 years of age. All three had to pass a formal interview in French at the commune.
9 is the minumum age for independent application, if a child was born here and has a C permit. My youngest arrived at 4 months, so she became eligible at 9 years and 2 months. With family applications kids are probably granted citizenship even earlier, but this needs to be verified.
If a parent / both parents apply for naturalization, they must include all children under 9 who live with them. If one parent gets the citizenship, then so do these children without other formalities, (no language tests, signatures, interviews, or ceremonies…).
If one forgets to incude the children, they will be sent (early in the process) a letter, asking them to confirm the addition of the children that they forgot to the process, or otherwise to explain why they want to become Swiss but they don’t want their children to become Swiss, and a warning that their application may be rejected if they insist without good reason.
The question was specifically for independent application, no parent applying.