Why the younger sibling speaks less heritage language

In one survey that King and Mackey report, the share of children who spoke the family's heritage language with their parents fell with each place in the birth order: 79% of first-born children, 66% of second-born and 43% of third-born. The authors explain it by time and exposure. First-born children get the most one-to-one parent time in the heritage language, and later children get more of the majority language from siblings and peers. This is REPORTED: a secondary citation that this site has not checked against the original study.

What the survey found

The survey, credited to Shin, covered 204 Korean-American families. The measure was whether the child spoke Korean with their parents. The gap is 13 percentage points between first-born and second-born, 23 between second-born and third-born, and 36 in all. The third-born figure, 43%, is 54% of the first-born figure (43 divided by 79).

Three limits apply. It is one group, Korean-American families, and the sources read do not say whether other languages show the same pattern. It compares groups, so it cannot say why your own two children differ. And it counts speaking with parents, not understanding.

A note on the citation. In its chapter on myths, the book cites Shin (2005). In chapter 5 it cites a 2002 report with the same figures. That may be two publications on one data set, or an inconsistency inside the book. This site has not resolved which, so it gives no year for the study (UNVERIFIED).

The reasons the book gives

King and Mackey's explanation has two parts. First-born children get the most one-to-one time with a parent in the heritage language. Later-born children get progressively more of the majority language from siblings and peers. The survey reports shares, not causes, so this is the authors' reading of it, and it is tagged REPORTED here.

Chapter 5 adds a point about school. When an older sibling starts school, that child brings home more of the majority language. The book uses the word "pollute", taken from a parent interview. The same change frees the older child's school hours, and a parent can use some of that time for extra one-to-one time with the younger child in the heritage language.

How the app treats birth order

For children saved in a household, the app reads each child's rank from birth years, and the oldest has rank 0. A later-born child gets a plan tip about protecting one-to-one time with that child, and a higher default of minutes a day: 30 for rank 0, then 5 more for each rank, up to 45. The 5-minute step is the app's choice, and no source read sets it (UNVERIFIED). On the standalone plan page you can instead say it yourself with an optional question: oldest or only child, second, or third or later. A second or later child gets the same tip there, but your own minutes stay as you typed them.

The app also flags when an older sibling is in school. In a household it works this out from birth years: a sibling born earlier who is currently 5 or older. Age is this year minus the birth year, unless you gave a birth month, in which case it is years completed, counting from the 1st of that month. That is a rough proxy, not something the parent stated. On the standalone plan page, a second or later child gets a box to tick instead: "An older brother or sister is 5 or older", which is your statement, with 5 as the app's rough guide.

ILLUSTRATION with invented birth years, run through the app's code in October 2026: three children born in 2019, 2022 and 2024, with no birth months entered. The 2019 child has rank 0, no flag and a default of 30 minutes. The 2022 child, aged 4, has rank 1, the flag on because the older sibling is 7, and a default of 35 minutes. The 2024 child, aged 2, has rank 2, the flag on and a default of 40 minutes. The flag's tip says to use some of the freed time for the heritage language, and adds that this does not happen by default.

What to do

1. Count each child separately. The audit works per child, so the hours a younger child spends with each caregiver show up on their own.
2. Give the younger child time alone with a heritage-language speaker, not only time in the group of siblings. The book's explanation rests on one-to-one time.
3. When an older sibling starts school, decide in advance how you will use some of the freed hours.
4. Look at the child, not only the rank. King and Mackey also describe temperament: shy or sensitive children tend to do better with predictable, low-pressure exposure such as reading and songs, and outgoing children with more conversation. The plan page has an optional question about this.

If one child's speech worries you in every language, ask a pediatrician or a speech-language professional. Birth order is not a diagnosis.

What is not known

• Whether other languages and other countries show the same fall by birth order. The survey was of Korean-American families.
• How much of the gap the school change explains, and whether any tactic closes it. No source read for this site tests that.
• Which year is right for the Shin study.