Liver fat and iron quantification is of growing interest. However, it is challenging and sometimes impossible to perform breath-hold MRI acquisitions in children. Using a breath-hold 3D Cartesian method as reference, a self-gating free-breathing 3D stack-of-radial liver R2* quantification technique was evaluated. Results showed that the free-breathing stack-of-radial technique accurately quantified fat even without self-gating, while free-breathing R2* quantification had biases caused by respiratory motion and self-gating was necessary for accurate R2* quantification in pediatric subjects. This technique has potential for accurate and efficient free-breathing quantification of both liver fat and iron in pediatric patients.