A child seat liner provides a comfortable, safe, and hygienic environment for a child seated in a seat such as a shopping cart or a highchair. Child seat liners according to various embodiments of the invention include padding around the leg openings, multiple storage areas for the caregiver, a continuous, elastic front edge for stretching over and gripping a handle of a shopping cart or a front of a seat, one or more sets of fasteners for securing the liner in a rolled-up position, and an adjustable strap that allows the liner to be secured to the back of the seat more securely.