Complex sentence: Pre-primary education (preschool education) embraces children between 3 and 6/7 years old, who attend kindergarten optionally, with the requirement that prior to starting school, children must attend a one-year pre-school program.
Split into simpler sentences: Pre-primary education (preschool education) embraces children between 3 and 6/7 years old. However, prior to starting school, children must attend a one-year pre-school program.