Try the fit in person
Have your 10-year-old hold several guitars while seated. Can they reach the first frets without stretching, relax their shoulders and wrists, and keep the instrument steady? A half- or three-quarter-size label is only a starting point, not a rule.
A first activity
Alongside melodies, try two accessible chords, such as Em and Am, and listen to the difference. Let musical taste help guide the choice of teacher and instrument.
Which guitar size for a 10-year-old?
It depends on the child and the model. Try different sizes and check reach, posture and how easily the strings can be pressed.