I don't see any reason for a child not to have a key for his/her own home..other than they may loose it..how young?... I'd say around the time they leave primary school.. or when you stop picking them up from school...it dosent mean you leave them alone at home but don't see any harm in them having a key to the door.
Sorry, when you said from an early age I though you were talking about young children, children of 5 or 6 years old.
Yes, I agree, when they leave primary school.



... and your Dad had the locks changed the next day 