Of the 223 infants, 54% were male, 45% were firstborn, and 13% were born more than 2 weeks prematurely.
Subjects were 101 healthy firstborn infants and their primary caregivers.
In this sample, there is no evidence that the gender of the firstborn child affected the vocabulary competence of the secondborn child.
For example, maternal reports suggest that firstborns have larger vocabularies and reach language milestones sooner than their younger siblings.
Some firstborns correct these errors by the time they begin to produce pronouns and do not show errors in production.
Twenty-four of the children were firstborns (8 boys and 16 girls).
We therefore examined language differences in firstborn and secondborn girls and boys.
Nineteen preterm infants (45%) and 17 full-term infants (41%) were firstborn.
