Sound and strings
A classical guitar uses nylon strings and often has a wider neck. Let the child pluck an open string and try a note at the first fret: can they reach without strain? Nylon strings do not make an oversized guitar fit.
Choose by feel
Compare smaller classical models in a shop even if they carry the same size label. Check how the body sits on the leg, fret reach and string height. Never fit steel strings to a classical guitar.
Must beginners start on classical?
No. Another guitar may suit the child better; consider comfort, musical interests and a teacher's advice.