Attorney here.
The original version of A New Hope should enter the public domain in 2072.
The Special Edition of A New Hope should enter the public domain in 2092.
The despecialized edition uses work from the special edition and would not be legally distributable until at least 2092. But as to your question on resolution, I do not believe copyright law would differentiate between a work bases solely on the published resolution. As the other comment suggests, A high res scan of the original A New Hope, if it exists, would be in the public domain in 2072.
Depends on the age of the child and also if the child understands that the parents have access to it and will make sure they are safe.
There is a healthy balance.