We started by getting three books of Shakespeare for children. The theory there being that if he knows the story well, the Elizabethan language will be easier to follow. We used: Tales from Shakespeareby Charles and Mary Lamb, Shakespeare Stories by Leon Garfield, and Beautiful Stories from Shakespeare by Edith Nesbit.
We read Midsummer Night's Dream in each of the books, and then we watched the 2005 ShakespeaRe-Told version. It was adapted for a television audience and uses modern English and a modern setting, so again, he became familiar with the story.
Next we checked out several version traditional versions of the movie.
So far, we've watched:
the 1999 version with Michelle Pfeiffer as Titania
the 1981 BBC version with Helen Mirren as Titania
Jack watched each version three of four times, and then we started reading some scenes along with the movie using a 1959 edition of the the Pelican Shakespeare Library. (I don't think it matters much which version you use, though older versions will have been better-edited and this in one case where a mis-spelled word can be very confusing.)
The next step is the start reading scenes together. Maybe tonight.
But meanwhile, Jack has been absorbed in the story and has been adding Elizabethan turns of phrase and Shakespearean descriptions to his already colourful vocabulary. (It also led us off into finding th story of Pyramis and Thisbe in Bullfinch's Mythology.)
I wish I knew of a local company doing this play in the near future -- that would be my ideal for the next step. Ahh, well. Movies will do for now.