about 老大‘s reaction to sibling: my encounter in library

last Sat we went to a local lib and saw a mom with a girl around 4 years old and a little boy around 1. the mom was busy reading to the girl and the boy was playing by himself. he fell form the bench and cried. later we saw the mother comforting him and showing him pictures on books. but while the mother was doing this, the bigger sister started pulling the book away from her mothers hands and pushing her little brother away. later we saw the mother reading to her again.
and the little one? he approached my husband. my hubby patted him and talk and smiled to him. he smiled back, very sweet smile. we talked about this for a while. such a sweet boy but seems a little neglected.