Does the stepfather beat the children? Children's mistakes can be educated, but why do you hit children in the face so hard? How long will this marriage last?
Moderate discipline is ok, but hitting a child in the face so hard is not education, it is simply a violent tendency. Look at the stepfather's attitude If he shows strong regret, he may not be able to control it for a while, but he can still maintain it. If he thinks it doesn't matter, leave early and don't let the child suffer any more.