what is a full size classical guitar
There are differences in the size of guitars, so it's hard to say there's just one standard. In general, you can sort guitars by the scale length, the distance between the nut and the bridge. If that distance is 24-26, the guitar is full size; 22-24 is 3/4 size and 20-22 is 1/2 size.
Decide whether to buy an electric, acoustic, or classical guitar. The most common guitar for a child's first is a classical style guitar. A classical guitar is an acoustic guitar with nylon strings. While acoustic guitars with metal strings are more common in the music industry, nylon strings are softer and easier for children to press down and strum.