Someone who is not the parent of a child can file a petition seeking non-parental custody. RCW 26.10.030. In theory, the petition can be filed by anyone, but normally it is filed by a family member, like a grandparent, aunt, uncle, or step-parent. The petition must allege that the child is not in the custody of a parent or that neither parent is a suitable custodian. RCW 26.10.030(1). Parents have a constitutional right to custody of their children. Mecum v. Pomiak, 119 Wash. App. 415 (2003). However, custody can be awarded by the court to a non-parent if both parents are unfit, or if the child's growth and development would be detrimentally affected by placement with an otherwise fit parent. In re Shields, 120 Wash. App. 108 (2004). The overarching purpose of the non-parental custody statute is to serve the best interests of the child. RCW 26.10.100. The burden of proving this by substantial evidence is on the petitioning non-parent. In re EATW, 168 Wn. 2d 335 (2010).