To determine the parents' ages at the birth of each child and the birth years of the children, we'll follow these steps:

1. Calculate the birth year of each child based on their ages as of November 9, 2019:

   • Eldest (26 years old):
     Born in 2019 - 26 = 1993.
     Since the birthday (May 11) has already passed, the birth year remains 1993.

   • Second oldest (24 years old):
     Born in 2019 - 24 = 1995.
     Since the birthday (October 12) has already passed, the birth year remains 1995.

   • Middle (16 years old):
     Born in 2019 - 16 = 2003.
     Since the birthday (January 15) has already passed, the birth year remains 2003.

   • Youngest (12 years old):
     Born in 2019 - 12 = 2007.
     Since the birthday (March 27) has already passed, the birth year remains 2007.

2. Determine the parents' ages at each child’s birth:

   • Mother's birthdate: February 21, 1967.

   • Father's birthdate: July 29, 1967.

   • For the eldest (born in 1993):

     • Mother's age in 1993: 1993 - 1967 = 26 years old (already had her birthday on February 21).
     • Father's age in 1993: 1993 - 1967 = 25 years old (his birthday on July 29 was after the child's birth on May 11).

   • For the second oldest (born in 1995):

     • Mother's age in 1995: 1995 - 1967 = 28 years old (already had her birthday on February 21).
     • Father's age in 1995: 1995 - 1967 = 27 years old (his birthday on July 29 was after the child's birth on October 12).

   • For the middle child (born in 2003):

     • Mother's age in 2003: 2003 - 1967 = 36 years old (already had her birthday on February 21).
     • Father's age in 2003: 2003 - 1967 = 35 years old (his birthday on July 29 was after the child's birth on January 15).

   • For the youngest (born in 2007):

     • Mother's age in 2007: 2007 - 1967 = 40 years old (already had her birthday on February 21).
     • Father's age in 2007: 2007 - 1967 = 39 years old (his birthday on July 29 was after the child's birth on March 27).

Summary:

• Eldest (born in 1993): Mother was 26, Father was 25.
• Second oldest (born in 1995): Mother was 28, Father was 27.
• Middle (born in 2003): Mother was 36, Father was 35.
• Youngest (born in 2007): Mother was 40, Father was 39.

Would you like a deeper explanation, or do you have any questions?

Related Questions:

1. How would the parents' ages change if the current date were different?
2. What would the children's ages be on a future date, such as January 1, 2025?
3. How would this problem change if the parents were born a year earlier?
4. What if one of the children's birthdays was later in the year than the current date of November 9, 2019?
5. How does this calculation change when considering leap years?

Tip:

When calculating someone's age, always check if the birthday has already occurred in the current year. This ensures an accurate age calculation.