I only ran away as an older kid. I was 11 the first time and made it several miles to my grandparents' house. I ran away several times over the next 3 years, including being taken home by police and leaving again the same night.
It was definitely a sign of something wrong in the home.
A few weeks ago, my 5 yo told me she was going to run away and never come back. Totally different thing.
I ignored it and dealt with the anger she was feeling at the time instead.