Placement question

There is a family that has two kids ages 8 and 6 who will begin cm next year? The 8 year old finished second grade but did not study any world history. He can narrate fairly well but did not have much exposure to literature. Should he begin with his sister and continue in Form 1 for three years or begin at a second or third grade and only spend 1-2 years in Form 1? This family is from and lives in Peru South America