There are many long-term positive associations between music lessons and your child's intelligence and happiness.
"Long-Term Positive Associations between Music Lessons and IQ"
"The duration of music lessons was correlated positively with IQ and with academic ability ...even when potential confounding variables (i.e., family income, parents' education, involvement in nonmusical activities) were held constant."
"Improvement In Social, Planning and Verbal Skills from Music Education"
"Test scores on inhibition, planning and verbal intelligence increased significantly in the two music groups over time as compared to the visual art and no arts controls. "
"Short-Term Music Training Enhances Verbal Intelligence and Executive Function"
"After only 20 days of training, only children in the music group exhibited enhanced performance on a measure of verbal intelligence, with 90% of the sample showing this improvement."