If you suspect trouble at home, approach moms in a cautious manner. I'm here for you. Think of how you would like someone to raise this issue with you. Don't feel you have to solve the problem by yourself. Figure out who on staff may be best to talk to the child or mom.
Role play among staff to work out the best way to approach the mom.
Realize that it is not your place to tell a mother what to do. If she confides in you, you can offer assistance. Recognize that she may not be ready to address the violent situation and this is not your fault. But remember that later on, when she is ready, she may use the resources you have provided. Be a liaison with outside agencies, organizations, schools, etc.