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Wow this is a hard one as when I grew up we were running around with no deadlines besides meals and be home before dark. Mind you my parents knew where I was with and who I was with.
But 10 and six might be a bit young for playing in park alone given the change in society. The village is no longer our protection when our children play, at best the are meek witnesses to a crime not our children's champions. So may 12 year old and a 8 to 10 year old in the park might not be so bad.