If you are concerned that your former partner is an unfit parent, you will need strong evidence to prove this. This could include police reports and school reports, as well as written statements, photographs showing signs of abuse, medical records and copies of any communications between you and your former partner.
Types of behaviour which could see a parent considered unfit for custody include:
A history of domestic abuse
Evidence of a drinking problem or substance abuse
Whether they can provide a suitable, safe home environment
Whether they have a criminal record