Joseph,
Society sets standards and government in the US is made up of society.
In this area children are permitted to walk to and from public schools alone as of grade 4. Prior to that they must be released by the teacher at dismissal to a parent, guardian or designated older child who is in at least 6th grade (approx age 11-12).
Again, in CT these are standards, not laws. DCF or a judge can be convinced that you have made a responsible decision eaving a 10 year old with a 5 year old for 2 hours in the afternoon or early evening, not that a 10 year old should be putting 4 younger siblings to bed for the night and parents not return until after 9PM