Step-siblings are children who become siblings through the marriage of one of their parents to someone who already has children. For example, if your mom marries someone who has a son or daughter, you and that child become step-siblings. This means you share a family connection, even though you are not related by blood. Living with step-siblings can be a unique experience. You might share a home, celebrate holidays together, and even go on family trips. While it can take time to adjust to this new family dynamic, many step-siblings form strong bonds and create lasting memories together, just like any other siblings.