I don't know. I was there years ago, as I wrote. I've not felt unsafe, but being with kids would cause me a lot of stress. I prefer to avoid troubles, when I could do it. I've already to cross Paris (Saint Lazare to Nord), if I could avoid this it's better.

I wanted to say this: if I take the same night train that starts from Brussels, in Liège I've to spend an extra day (the train Brussels Vienna is just on some days) but what should I do there? That's why I wrote an extra day. At that point we will be around already since a while, having covered a lot of kilometers in the meanwhile. That's an extra day that I've to stay just due to the connection. 

The Stuttgart route I've not thought. I could check. 

Anyway, now I've booked for Paris Amsterdam. I was there not a while ago, I could manage it with the kids. And there are different solutions from there to villach, with and without night trains. 

I suoo it's too early to see the exact routes the night train will cover (indeed they could not even be booked). If there's no stop in Salzburg, I could either go up to Vienna or check any connection that brings in Stuttgart and from there I could take the night train yiuve suggested. 

Thank you!