Stay with Sister — Steven L. Layne

Big Brother finds out that not all babies are the same. Big Brother learns that not all little siblings are the same when his parents bring home a baby girl. He thinks he learned all about babies when Little Brother was small. However, Sister is very different. Other things are different too. Big Brother is old enough now to help keep an eye on the baby when Mommy and Daddy are busy and watching after Sister is not as easy as it sounds. But despite all the trouble she causes, Sister finds her way into Brother's heart, and that is where she will stay.