If you live in Japan as a spouse of a Japanese citizen and have children, not all of your children might be Japanese citizens yet.
If you have 3 children, for example, and 2 of them are Japanese citizens, but the rest is a foreign national who is waiting to receive a visa which allows relatively free activities in Japan, there is one thing to heed.
The children who have Japanese citizenship can go to a public school without any problem, but the child of a foreign national cannot if, for example, the child is staying in Japan as a short-term visitor. Since these two children having Japanese citizenship go to a public school, that public school could accidentally allow the rest to go as a sibling. In fact, this thing has actually happened already.
If the child of a foreign national wishes to go to a Japanese school in this case, that child needs a student visa since going to a school as a short-term visitor is an activity not allowed under the current status. The consequences will be serious, so please beware.