The claim "listening to classical music as a baby makes you smarter" is very misleading. Infants listening to classical music does not directly lead to their IQ being higher in adulthood. In the article sourced, they claim that when babies listen to classical music, "they're not just hearing sounds; they're experiencing a world of emotions without words" (Jarret Webster 2018 ). But many studies counter this idea and show that interacting with infants, by talking to them and playing music with words, actually stimulates their brains more and leads to better development.
A review study done by the Federal Ministry of Education and research conducted by a group of musically inclined scientists declared the phenomenon nonexistent. "I would simply say that there is no compelling evidence that children who listen to classical music are going to have any improvements in cognitive abilities; it's really a myth in my humble opinion" ( Rausher ). Scientists argue that the real key to a "smarter" child is to interact with them as much as possible. Infants listening to words is far more beneficial to their growth than sounds. "It takes away from other kinda of interaction that might be beneficial for children, such as playing with them and keeping them engaged via social activity. That is the key to a brilliant child, not the symphonies of a long-dead Australian composer." ( Chabris ) Fact or Fiction?: Babies Exposed to Classical Music End Up Smarter | Scientific American
Additionally, Harvard University conducted a study about this theory to ultimately conclude that music does not enhance their intelligence and that this is simply a myth. They also state that "Although it is true that putting on classical music in the background does not boost intelligence, but introducing children to music in an active manner, especially at a young age, will help with learning development and other skills." ( Isaiah Crooks ) Does "The Mozart Effect" Actually Work? - Classics 4 Kids
Overall, classical music alone does not enhance an infant's odds of being intelligent in the future, but interacting with a child and even playing any sort of music (preferably one with words ) heightens the activity in their brain and could potentially lead to them being intelligent in the future.