Many adults get them wrong as well. I wasn't clear until I thought about how to teach my daughter about them.
It is actually about statements, i.e. whether a statement is about a fact, or just an subjective opinion. A statement about fact can be objectively verified to be true or false, but a statement of opinion is subjective, so you cann't say it is true or false.
Example:
Statement about fact:
1) Earthquake happened in Japan this year. (True)
2) Earthquake didn't happen in Japan. (False)
3) There will be no Earthquake next year in LA. (can be verified next year)
Statement of Opinion
1) Earthquake is terrible. (terrible is subjective)
2) Earthquake kills a lot of good people. (good is subjective)
Hope this helps.
