Kilted Kids do the Darndest things...

[OFCJAX]

You could easily add a small pocket onto the under apron. Just find a piece of fabric that matches or compliments the tartan cut into a rectangle, fold over hem the top right corner at an angle to allow the hand to slip in, and fold over the remaining edges and sew them to the right hand edge of the under apron.

Done.

[Standard]

You could easily add a small pocket onto the under apron. Just find a piece of fabric that matches or compliments the tartan cut into a rectangle, fold over hem the top right corner at an angle to allow the hand to slip in, and fold over the remaining edges and sew them to the right hand edge of the under apron.

Done.

Good idea, sounds like a good fix for your son's problem without having to worry about a sporran for daily wear at this age.