My OH has two kids from a previous relationship. The boy, 13, lives with us, and the girl, 11, lives with their mum. We have both kids alternate w/ends and their mother has them the other w/ends. They're really great kids and we all get along really well. They seem really pleased and excited about having a little sister. I just wondered if anyone has any experience of step-kids and new siblings and any advice on how to make sure that our - reasonably happy - family unit doesn't get too upset by the new arrival!