Yoto icons are 16x16 pixels on both the large Yoto Player and the Mini Yoto
Click on the track icon in the playlist editor to choose a new icon
Upload any image and it will automatically be converted to the right format. (16x16 pixel images will look closest to the original)
Find thousands of icons at Yotoicons.com
Create your own icons using any art package/app that allows for single pixel colouring. (Examples include 8 bit painter, Microsoft Paint)
Or… get the kids to colour a grid on paper (or in a spreadsheet) and convert it to an icon by uploading a photo. Find more info here on Yoto Space (scroll down to the 4th row)