Designed to provide ergonomic support for growing infants or toddlers whose legs are no longer supported (knee-to-knee) by the carrier in the narrow seat position. Baby is ready to move up to the wide seat when he or she can sit comfortably in the seat with the fabric extending to, but not beyond, the knees (approx. 18 months clothing size). Baby's knees should be able to swing freely, without any bunching of fabric behind knees. Readiness for wide seat is determined by femur length, and not weight or age. Do not carry small infants and newborns in the wide seat position - use inward narrow seat position or wide seat fetal position.