It is a longstanding assumption that listening to classical music benefits young children, even while in the womb. A former governor of Georgia even went as far as playing Beethoven's "Ode to Joy" to state legislators and commenting that they may "feel smarter". This incident sums up the popularization of the Mozart Effect and the false pretenses that went along with it.
Products like the one above sell to people that believe that their children will become more intelligent as a result of listening to classical music. However, saying classical music "increases intelligence" is greatly overstating the evidence. Science does say that classical music at a young age can increase spatial temporal reasoning in the short term.
The evidence is conflicting, however, which means that the Mozart Effect should be taken with even more skepticism. A study by Rauscher, Shaw, and Ky in 1993 showed that classical music had no significant effect on spatial intelligence, but ScienceBlogs.com begs to differ, as shown in the graph below.
Some studies even delve into analyzing the tonality (major or minor) and tempo of music and comparing, but the overall effect is still up for debate. It is known that the Mozart Effect does not increase overall intelligence, however, it may be slightly significant in spatial intelligence. Future studies will give us more knowledge of course, but parents should not rely on simply music when educating their young child.