A squabble is a fight but not necessarily a serious one. When we squabble, we have a little argument, probably about something not too important.
Do you notice how squabble sounds kind of funny? That's a clue that a squabble is not the most serious kind of argument or fight. A loud, screaming fight would never be called a squabble. A small, silly discussion about something small or trivial is more of a squabble. Friends and family members squabble all the time.