@article{ref1,
title="Social and play responses of first-born and later-born infants in an unfamiliar situation",
journal="Child development",
year="1968",
author="Collard, R. R.",
volume="39",
number="1",
pages="325-334",
abstract="<p>[Abstract unavailable]</p><p>Language: en</p>",
language="en",
issn="0009-3920",
doi="",
url="http://dx.doi.org/"
}