How much you teach your kiddos about Memorial Day will largely depend on their age and maturity. It may also depend on if you live in an area with a lot of military or not. You will have to make that determination. Here is a book all about Memorial Day! Print off the pdf version here!
I have specifically made the pages with varying levels in mind. Therefore, you may not use all the pages. It really depends on your audience. Print it off, talk about the text and pictures, put it together and read it each day.