How do I teach the violent passages to children?

Practically: check the immediate context first, then compare the parallel passages. You are far from alone in this. I had no answer for a very long time. Traditions answer this very differently, so ask in your own community too.

There's a long history here, with the argument running from the fourth century onward. It's fine to carry the question unresolved for a while. Tracing how the early church handled it locates the modern debate quite usefully.

It may be worth questioning the premise of the question itself. Worth adding: a non-canonical text treats the same theme and the comparison is illuminating.

The short answer is that scripture itself does not settle this; several readings coexist.