A key resource is the Home Office policing policy which includes the PACE codes and statistics.
For resources about Stephen Lawrence or policing and ethnicity, search the Library Catalogue for police racism or police ethnic minorities
There are lots of resources in this area but do be aware that many provide 'alternative' views - make sure you evaluate any of the resources you use for their academic content, authority and reliability.
NSPCC - resources on child trafficking and modern slavery
Every Child Protected against Trafficking - reports and guidance