How can I write a thesis on the relationship of the original Grimm works & modern day adaptations?I am supposed to write a research paper for...

I think you are correct in assuming a relationship between
cultures and their literary productions. In the case of the Grimm brothers, some of the
tales they collected go back before the 19th century. Also, many of the tales were
circulated in an "oral" society--that is, they were not written down or "published"
prior to the brothers' collections, so there are many "variants" or different versions.
Also, the brothers edited the tales in their collections to make them more "literary."
The particular cultural values at certain times in history also dictated what could and
couldn't be said or written publicly. Disney has more or less followed the same
process--changing the fundamental story so that it appeals to today's audiences. In some
versions of Hansel and Gretel, for instance, in the published works, the ending has been
"sanitized," so that the witch isn't put into an oven, there is no wicked stepmother,
and so on. If you compare several variants of a tale with their time periods, and
perhaps do a little sleuthing as to the standards of child rearing during those eras, or
an older version of a tale with the Disney movie in order to see what is acceptable or
not according to ratings and critical reviews today, you will have a workable thesis. Be
careful in your research--in folk tales, there is no such thing as an "original"!  Good
luck!