The standard answer to this question is an unqualified yes, most children should learn to play a musical instrument. Children learn discipline from the rehearsal process, self-expression from performance, and social interaction from group studies. A child can definitely benefit from learning to play music at an early age, since many professional musicians credit their early experiences with developing a life-long passion for music. Even if a child discovers other interests later in life, the discipline required could prove useful in other situations.
That's the good news. There is another side to the musical instrument question that many parents don't discover until it's too late. Allowing a child to learn to play an instrument also means a parent needs to prepare for repetitive scales, loud noises, and frequently missed notes. A child's interest in an instrument, especially a loud or amplified one, is destined to involve the entire family, whether voluntarily or involuntarily. The rehearsal process is a vital part of learning to play, but one child's rehearsal room may often be another man's den or basement.
Parents should also understand that a quality instrument can be a expensive investment, and a child's interest in any project can be notoriously variable. Before allowing a child to learn a musical instrument, consider whether the child seems enthusiastic enough to stick with it for several years. Families on a budget may want to consider using the family piano for music lessons or investing in a used instrument until the child's interest can be gauged. Investing in a musical instrument used for band performances, such as a trumpet or clarinet, may also mean investing in band uniforms, travel expenses, and accessories.
Another consideration is the cost and availability of professional instruction. Finding an affordable piano or guitar teacher may be a matter of contacting a local music store, but a child may have an interest in an instrument for which local instruction may be scarce. There are now a number of self-help instructional materials available online or through larger music stores, however, so a child may be able to teach himself the basics of playing without the need for formal lessons. Many schools also provide extracurricular music programs and instruction, but parents should understand this may involve picking up a child after practice and transporting him or her to out-of-town performances.
Children should definitely be encouraged to try out different artistic outlets, including music, theater, creative writing, and dance. If a young child shows a clear interest in a toy musical instrument, then parents may want to consider taking that interest to the next level. Pressuring a child to take up music for other perceived benefits, however, is rarely a good idea. Every child should have the right to pursue a creative outlet based on his or her personal interests and skills, and if it happens to be learning an instrument, then parents should understand it takes time and practice to develop solid performance skills. A parent's role in a young musician's life may be to push him or her to a higher level of performance.