You an apply for a non-molestation order, under the Family Law Act 1996.
A non-molestation order is a court order to prevent a woman�s partner from assaulting, pestering, molesting or threatening her or her children. It can also have very specific instructions in it to suit her particular case; for example, it could order her ex-partner to stop telephoning her or pestering her at work. She can apply for a non-molestation order against someone if she is associated with them. For the purposes of the Act, you would be considered an associated person as you were married to her ex husband and you have children together.
A non-molestation order is granted for six months or for an indefinite period. If your ex husband breaches the terms of the non molestation order, it would be an arrestable offence.
I have added a link to help you with further information.
http://www.newhamdvf.org.uk/civil.html