A story in the news today provides an excellent fact situation to talk about what the teachers involved in this incident might expect to happen and where they would look to get help. Not a lot of detail is provided by the story in the Waco Tribune-Herald, so this discussion is merely hypothetical and speculation, but I'm sure all teachers can easily identify with the potential for something like this to happen in your own school. The phrase "unsupervised" stands out in the headline. For a teacher, that's often the start of scary things happening.
This kind of playground accident is also what teachers are often worried about happening. So let's consider all the worst case scenarios. The parents of the injured students might try to sue. Suppose the students normally would have been supervised, but for some reason the teacher that should have been present, was not.
State law protects the teacher from any liability unless excessive force was used in the disciplining the students. Since this did not involve discipline, the teacher has immunity from any liability under state law. The administrators responsible for supervising the teacher who was absent from her post are probably also immune from liability under this same state immunity statute. If the parents want to sue, they will literally have to make a federal case out of it. But federal case will involve only the district or its "officials."
This means the parent will have to show that the school district or its officials who were responsible for setting policy somehow violated the students constitutional rights by not having supervision available. If the parents could figure out how to make this claim (and it's a big if, but possible if the facts were right), they would still have to sue either the district itself, or some individual employee who was responsible for setting policy. Classroom teachers will rarely fit this criteria. So, if the parents' try to sue because of their child's injuries, the classroom teacher who left the student's unsupervised would likely be either immune from liability or would not be the "responsible party" under federal law. Either way, it would not be necessary to call on any liability insurance.
On the other hand, if the teacher who was supposed to be supervising had left her post for a reason the district thought was not sufficiently reasonable, then the teacher could be disciplined. That might mean anything from a write-up, to a lowered appraisal, to a contract non-renewal. If any of those things happened, the teacher would need to have employment rights help in the form of an attorney or other trained representative. If she belongs to one of the teacher groups, she could get help through their employment rights defense/protection program.