A sibling contest is when a pookie (usually one that has already been adopted) has a contest for who will get to be their new wista/broder (sister/brother). If the pookie has already been adopted, then their mumu/duh duh (mother/father) usually hosts the contest. If they have not been adopted, then the pookie will
host the contest.
Typically, the host chooses categories, e.g. princess, movie star, or superhero. The pookies dress up or act as to the category.