J.S.
It's really up to you when you tell people socially.
As for the childrens' teachers I always tell them whenever there's a big change in the household dynamics or family situation. For instance the girls' teachers all had to be notified when my FIL passed away in October and how it was affecting them, and it helped explain some behavior/emotional changes in school. My husband lost his job at the end of March and I had to let the teachers know about that too because it's been such a big change and transition, especially for my daughter with Autism, that they appreciated that heads up too.
If I were separating or divorcing or having an especially difficult time in my marriage, I would feel obligated to bring it up to the girls' teachers and/or guidance counselor/school psychologist. If you do this, then you can also request that the kids get some time to talk things out with with the counselor too.