The High Contrast option provides a dark background for the picture mode, that helps children with visual challenges. Turn ON the High Contrast option(under Picture settings) to enable this. The other settings that help are Zoom and Pictures per screen settings, which enlarge picture sizes.
Set up the following options:
Settings > High Contrast = ON - Click to know more - How do I turn on the High Contrast for the app?
Settings > Zoom = ON - How to turn on Zoom?
Settings > Caption (text) Size = Large - How to change text size?
Settings > Pictures per screen : try with 2 or 3 and gradually increase till the child is comfortable with identifying the picture and fix it at that level. How to change Pictures per screen?