well 134cm is 4ft 4 & is bang on average height for his age, so straight away I can tell you that a 43cm c-c sloping geo frame would be too big (That is the size of the ISLABIKE Luath 26)
He is more likely to want something in the 36-38cm range but bear in mind he likely grow 14-16cm in the next two years which will take him into the very small framed 700C bike territory.
Here's an interesting article you might want to read. http://swinny.net/Cycling/Kids_on_Bikes ... cing-Bikes
Best of all is to get him on a bike, measure the top of the saddle to the floor in a comfy position and the reach from the centre point of the saddle(where it would intersect with the seat tube) to the handlebars, again making sure that the reach is comfy. Lastly his inside leg if requiring to stand over the top tube.
You can then ask any sellers if the bike they have fits to those dimensions with leeway either side.
1958 Carlton Super Python
1990's Gitane VITUS GTI Triple Butted
1996 Raleigh Titanium Special Products Division
2007 Specialized Globe Pro
2007 Specialized Globe Expert Ultegra 6700
KTM Strada 6000 Carbon Dura Ace 9000