When choosing a first guitar for a kid, the three most important things to think about in my mind are: intonation, comfort, and look. Lets talk first about intonation.
When it comes to sound, the most important thing when you learn how to play is not necessarily the quality of the sound, but its accuracy. When a child learns to play, he or she trains not only their motor skills, but most importantly also their hearing skills. For this it is important to have a guitar that has decent intonation – namely a guitar that produces the right pitch across the neck. This way the child’s ears will hear the right tones and will develop a proper intuitive musical understanding of the relationship between the different sounds – an extremely important aspect of learning to play any music. Unlike pianos, guitars need to be tuned constantly, and require at least some minor adjustments almost every time they are being picked up to play. It is very advisable to have some kind of tuning aid device that the child knows how to use. The simplest one is a tuning pipe that can produce the six distinct open position string notes of a standard guitar tuning. You tune the guitar by comparing the sound of the pipe to the sound of each guitar string. However to do this you will need to be able to compare pitch by hearing. You could also use a keyboard for this purpose. An easier option is a digital guitar tuner – a device that shows you with a visual dial the proper pitch for each string. Any of these methods will work, as long as you make sure the child knows how to do it and always plays a properly tuned guitar. Like I said, a guitar’s tuning needs to be adjusted practically every time it is picked up to practice. You cannot afford to postpone this until you have a lesson with the teacher and let your teacher do it for you.
A good guitar should have at least decent intonation, that is, it should not have to much deviation from the right pitch across the neck. The quickest way to check the intonation of a guitar is, after tuning it, comparing the harmonica on the 12th fret to the fretted sound on the same 12th fret. YOu get the harmonica y touching the string lightly just on top of the 12th fret, picking the string and releasing your touch immediately after picking the string (it takes some practice). The resulting sound should be a light ‘airy’ resonant sound. Compare this to the sound when the 12th fret is actually fretted. If they sound reasonably similar in pitch that means that the intonation is at least reasonable. Do this for all 6 strings. Another place where you can quickly check the intonation of the guitar is, after tuning the guitar with a tuner, by fretting the 5th position and comparing it with the open position of the next string and seeing if the pitch sounds reasonably similar. When you use this method do not fret too hard. Doing so would shift your pitch higher, and more so with a short scale guitar. On general you should bear in mind that guitar, similarly to piano, is essentially a compromise instrument in terms of intonation. That is, it could never be tuned to mathematical accuracy. All we are looking for is a reasonable enough compromise that will sound decent enough.