first child versus later children

[Yuriko Oshima-Takane]

Our study on the language development of first-born and second-born
children of English-speaking families (N=32) showed that second-born
children acquired the correct use of first and second person pronouns
earlier than first-born children, although they did not differ significantly
in general language development either at 21 months or at 24 months of age.
The results together with the findings on their linguistic environments
support our claim that second-borns benefit from overhearing the
conversations between caregivers and older siblings. In particular,
overhearing the systematic shifting reference of personal pronouns
in conversations between their caregivers and older siblings is
crucial in understanding the correct meaning of second person
 pronouns.  These results are consistent with our previous experimental
findings and recent computer modeling results.

Oshima-Takane, Y. , Goodz, E., & Derevensky, J.L. (1996)
Birth order effects on early language development: Do secondborn
children learn from overheard speech? Child Development, 67, 621-634.

For other relevant references, please see:
http://www.psych.mcgill.ca/labs/lnsc/html/person-yuriko.html

Yuriko Oshima-Takane