Your search results should reflect the intersection of multiple topics
Broad Topics = Media, Violence, Children
Narrower Topic = Violence in the media
Focused Topic = Media violence and children
The intersection of your broad topics is your research focus. When searched together, these terms will yield more relevant results.
Building Your Thesis
From your broad topics, build a vocabulary of similar or related search terms you can substitute if needed when searching online. Additionally you may find this will help you narrow your scope when developing your thesis. For example:
media = television, film, video games, comics, music, etc.
violence = assualt, attack, fighting, etc.
children = toddlers, teenagers, adolescents, etc.
Using your chosen broad or narrower topics, create your research (thesis) statement:
What are the effects of video game violence on teenagers?, OR ...
Video game violence adversely affects (or does not adversely affect) teenagers.
Your objective? Using evidence found in your research, seek to prove your research statement OR answer your research question.
These are your search terms you will use to locate information resources. Consult a thesaurus to add synonyms to these terms, if necessary.