To get a good fit, both the shape and the size of the shoes should conform to his feet. The widest part of the foot may not be seated in the corresponding widest part of the shoe, even though they may be of the same width. Also, the width of the heel may not fit the heel of the shoe. However, this does not mean that one cannot find shoes that are comfortable and that generally conform to the shape and size of the foot. Foot size increases with standing as well as with the time of day.
Feet are slightly longer and wider at the end of the day.
The average adult foot increases 4 percent in volume from morning to night. While no formal study has been done in children, I believe that proportionate increases could be expected. I would therefore recommend that you shop for shoes later in the day when feet are at their largest. Even while you are looking at the different shoes in the store, keep in mind the shape of the shoe that you should be looking for. The shape of the shoe is determined by the last which is the model from which the shoe is made.