How can I save children from getting physically abused by their mother

Kindly provide me the legal advice and suggestion when the woman beat her own children of 6 to 9 years with dangerously and threatened to kill them only because of small reasons like children playing late night etc.Its not once but so many times.After trying to convince her by husband and her mother not to do so not yet stopped.She abuse & misbehave with husband & not behave properly with husbands family. Its the case of women violence not husband.Any Legal suggestion counselling and protection of kids form this type of violence which may be danger for their life or development in future.If she killed any child which is possible when saw her behave in anger then whats the use of the law or suggestions.She had two children.