Your child wants to make music, and the choice comes down to piano or guitar. Both are lovely first instruments and neither is right for every child. This guide sets out the practical differences so you can decide together, ideally with a teacher's advice.

Start with what your child wants

Your child's own interest deserves real weight. A ten-year study by Paul Evans and Gary McPherson, published in Psychology of Music (online in 2014), followed 157 children who started learning an instrument at around seven to nine years old. Children who pictured themselves playing for the long term tended to achieve more and keep going for longer than children who expected to stop soon. The study was not about piano or guitar, but it suggests that how a child sees themselves as a musician matters.

So ask them. Listen to some piano and guitar music together and, if you can, let them try both.

Age and hand size

The piano has one clear advantage for young beginners: pressing a key makes a clean note straight away. The keyboard itself cannot shrink, though. Thomann's guide to instrument sizes puts it simply: "A piano can't really be made smaller."

Guitars, by contrast, come in fractional sizes such as 1/4, 1/2 and 3/4, so a child can play an instrument that fits. As a rough guide, Thomann suggests a 1/2 size for many children aged about 7 to 9 (roughly 120 to 140 cm tall) and a 3/4 size for about 10 to 13 (roughly 130 to 150 cm). Other retailers, such as Normans, give slightly different age ranges, and both say that arm and finger length matter more than age.

Guitar asks a little more of small fingers, because the strings must be pressed firmly to make a clear note. Some teachers start very young children on piano for that reason, while others happily start them on a small guitar, so ask what local teachers prefer.

Nylon or steel strings

For young guitar beginners, nylon strings are usually the gentler choice. Thomann explains that nylon strings are "much softer than the steel strings" used on western acoustic guitars, with "a lower tension, so that pressing down is easier". Classical guitars, which use nylon strings, also have relatively wide necks, which Thomann says makes them easier for beginners to grasp. Steel-string acoustic guitars are popular for pop and folk songs, but their firmer strings take more getting used to.

Keyboards: the features that matter

An acoustic piano is a big purchase, so many families start with a digital piano or keyboard. Not every keyboard is equally helpful for learning. Touch-sensitive keys, which Sweetwater describes as playing "at different volumes depending on the speed you play them", let a child learn to play loudly and softly. Weighted keys feel closer to an acoustic piano, and Sweetwater's beginner guide says weighted keyboards are "best for beginners who also want to play the acoustic piano".

Exam boards set similar standards. For its digital (video) exams, Trinity College London allows digital pianos at all grades if they have a "touch-sensitive, weighted keyboard" and enough range for the pieces, and allows electronic keyboards up to Grade 3 if they are touch-sensitive. Keyboards with these features tend to cost more than the most basic models, so it helps to plan for that if your child chooses piano.

Other things to weigh

• Space and noise: a digital piano can be played through headphones, which Sweetwater notes suits quiet practice. A guitar is easy to carry to lessons.
• Teachers near you: find out who has space, which ages they teach, and whether they offer piano, guitar or both.
• Exams: if graded exams appeal, look at the board's instrument rules before you buy, so the instrument will still suit your child at Grade 3 and beyond.

There is no wrong choice here. Whichever instrument your child starts on, the habits they build now, such as listening carefully and practising little and often, will help with any instrument they pick up later.