I visited Belgrade and Nis last year, it is a safe and peaceful country compared to Paris or Marseille. A quiet place to live with children and family.
Unless you don't mind round the clock air pollution, violation of human rights, hybrid political regimen (not a democracy) and coruptation in every public instutiton, then yeah it can be pretty okay place for a family
Grass is greener. If you lived in a city all your life you know all the seedy areas and bad stuff happened to you in that city. If you go travel to another city and see the touristy places it will feel splendid and almost for sure nothing bad will happen to you because of statistics.
I lived in Belgrade and Nis for half a year. Did not feel too safe if you go far from center or too close to main bus station. I think I liked Novi Sad more than other two.
Regarding peace, I gathered that many people there support Putin's war so there's that. But people are different. Serbs specifically have an axe to grind because of the bombings (of course their government also committed a genocide but whatabout this, whatabout that).
Almost everywhere in the former Yugoslavia is more safe than in the West. But it is not only safe, you will very easily make friends as people are much more open to forming friendships. Belgrade is one of my favourite cities. Never been to Nis
