Turn your garment inside out. This will minimize the amount of abrasion that the print will encounter with other garments in the wash.
Wash the garment in cold water using a mild detergent.
Do not use bleach!
Remove the garment from the wash immediately, and allow to air dry. If you are going to tumble dry, use the air only setting. By doing this over the life of the garment, you will avoid unnecessary shrinkage. Shrinkage is usually a bad thing, especially for the boys.
This garment does not require ironing. If you are going to iron your garment, do not iron directly over the printed area.
Or... don't wash it at all. Just buy a new one everytime you feel the need for a clean one! We have so many to choose from that you could literally wear a new shirt every single day of the year!