From this page you can download leaflets about supporting a child who has witnessed domestic abuse.  The set of ten leaflets cover ages from baby to teenager and other related topics. 
These leaflets were reproduced for Cambridgeshire from the originals with kind permission of West Mercia Women's Aid
The Family Rights Group have a webpage dedicated to young parents who are experiencing domestic abuse.  The site contains information and advice and also answers some questions you might have.