Size Guides: Measuring Guidance:

Take a shirt that the player knows fits them and lay it face up. Measure from one side (under the arm) of the shirt across the chest to the other side. This should give you a measurement in inches that matches a size on the above size guide.

Icon also produce Pennine Juniors Teamwear which can be seen / purchased here: https://iconsports.co.uk/my-club-zone/football/pennine-juniors-fc-teamwear