my son logan hand a street-stroller back in the day. (ill try to find a pic and post it for you) anyway, we took old handwheels off of an old machine and milled them to accept a rubber o-ring type pedal car tire. here is a pic to a similar handwheel that we used...
here is a link to some pedal car tires, wheels and hubcaps
http://www.speedwaymotors.com/m/540_Pedal-Car-Wheels-Tires-and-Hubcaps.html