Can multimedia educational materials really help a baby’s development?

No. Their have been studies done where they compared babies who watched multimedia educational materials (baby einstein) and babies who interacted with people/their parents, and found that babies who interacted with people/their parents developed faster. There is no substitution for human interaction.
No. There is no "multemedia" tha can substitute loving attention from parents. Everything your baby needs to learn, he will learn via interaction with the people that surround him. There is nothing more interactive than parents talking and playing with a baby.
No. There is very little evidence that multi media materials will help the development of a baby any more than good old-fashioned physical interaction. Some experts feel that it actually gets in the way of more beneficial stimuli. The american academy of pediatrics recommends no t.V. Or videos before the age of 2.
No. The american academy of pediatrics recommends that infants under 2 have no screen time, and no more than 2 hr/d for older children. You will do so much more for your child if you play, interact, read with him. Talk and describe what you see, "look! A red ball". Describe color, shape, texture, size, compare similarities, differences. Studies show 1:1 interaction produces smarter children vs media.
No. Babies have been developing just fine over the past 100 years without the recent multimedia materials. Since the human species changes/evolves very slowly, I am sure that today's babies can develop just fine with traditional non-electronic materials.
No. The jury is still out, but the studies so far show a baby who interacts with parents with things such as just reading to them fair better and have higher IQ than multimedia exposure. This applies certainly for the first year of life, but then the answer gets hazier. If you are talking a baby under age one, parent time with one on one play, looking at picture books and reading to the baby is best.
No. "developmental" videos have not been shown to increase scores on tests of learning or intelligence in measurable ways. This means that one can save (a lot of) money as these products have not been shown to be helpful. On the other hand, parents seeking stimulating products as an alternative to tv aren't wrong. The real point is that "screens" should never substitute for in-person face-time.