It would do no harm to tip off a School Counselor or Therapist at the kids' school.
They know how to check things very discretely and if there is any problem going on at the home (yeah, right, "if," huh?) they are required to act upon under what is called a "Duty to Report." That will get the correct authorities involved.
After that, you can follow up and see if there is anything you can do to help.