I was talking with my wife (a native polish speaker) to get clarification of this word, and she said the same. In English, the verb "to rear" is a closer translation, according to her. You can raise children, farm animals, and vegetables, but you can only rear children. Is "rear" an accepted translation?
The present progressive is for an action that is happing at or around now, but it has some other uses incuding for actions that have been started and not finished. For most parents "They are raising children" is correct. For foster parents who repeatedly raise children you could use present simple.
English is not my first language, so... Is "They are bringing the children up" wrong?