26" bmx bikes were somewhat common during the 80's. These is the only people that I know of that still make them.
http://www.firemansbikes.com/original.htm

Most manufacturers offer a bmx cruisers with 24" wheels and usually just a rear brake. I'm not sure a bmx bike is the best for commuting. I ride a singlespeed MTB. It's alot like a bmx but has brakes front and rear and a frame that lets me get proper leg extention while seated. I'm not sure most bmx's allow this. Redline makes a singlespeed MTB called the Monocog that's about $350. Your son might what to check it out.