Let the child try the instrument
Check that the child can reach the strings and first frets without stretching. An oversized guitar or one with high strings can be frustrating. A teacher or guitar shop can assess the neck and string height.
Keep practice short and playful
Play a familiar melody for a few minutes or find notes on the interactive fretboard. Alternate between listening, singing and playing. Stop if fingers or wrists hurt; press just behind the fret rather than squeezing harder.
Choose and practise together
Don't rely only on age or a size label when buying: reach, height and preference vary. Try different instruments and involve the child in the decision. At home, a guitar, a tuner and a calm practice space are enough to start.