Smart people often play musical instruments as well, so that has led to research trials seeking a causal link between music training and improved cognitive and academic performance, but they have reached conflicting conclusions. Some did suggest - a lot of bad epidemiology happens with that word so caution is warranted - that there may be a link between music training and better cognitive and academic performance. Others found no impact.
Meta-analysis to the rescue. Maybe, since those have inherent weaknesses, right along with the studies included. The authors re-analyzed data from 54 previous studies conducted between 1986 and 2019, including a total of 6,984 children, and found that music training appeared to be ineffective at enhancing cognitive or academic skills, regardless of the type of skill (such as verbal, non-verbal, speed-related and so on), participants' age, and duration of music training.
When comparing between the individual studies included in their meta-analysis, the authors found that studies with high-quality study design, such as those which used a group of active controls - children who did not learn music, but instead learned a different skill, such as dance or sports - showed no effect of music education on cognitive or academic performance. Small effects were found in studies that did not include controls or which did not randomize participants into control groups (ones that received different or no training) and intervention groups (ones that received music training).
Giovanni Sala of Fujita Health University, Japan, the lead author said, "Our study shows that the common idea that 'music makes children smarter' is incorrect. On the practical side, this means that teaching music with the sole intent of enhancing a child's cognitive or academic skills may be pointless. While the brain can be trained in such a way that if you play music, you get better at music, these benefits do not generalize in such a way that if you learn music, you also get better at maths. Researchers' optimism about the benefits of music training appears to be unjustified and may stem from misinterpretation of previous empirical data."
Trying to make kids smarter was never a good reason to get kids into music. It can give kids a new social circle, which improves social skills, and it builds self-esteem. Since music is also math, it can't hurt.
But too few quality studies have been conducted to reach a definitive conclusion about possible positive effects of music education on non-academic or cognitive characteristics. So get them involved because they want to be involved.