D..
My opinion is that they do not make your baby smarter. However, the people who would buy them for their children are the ones who pay lots of attention to academics, and their babies are smarter because their parents don't ignore them.
Now, it follows that mothers like ME who know that it's a waste of money, also have smart children because we care about academics too, and we don't ignore our kids either.
Old fashioned tried and true methods of engaging a child in age appropriate manipulatives, playing music for them, talking to them, reading to them, etc are what help a child to learn. Not a bunch of baby Einstein products.
Dawn