I bought an inexpensive casio keyboard which came with an instruction book. Since my kids somehow made it to 9 and 11 without ever learning to sing (what the heck are they doing in the public schools?!) we are working on singing Do-Re-Mi (scales) on tune -- a not insignificant task! Then we will progress to singing songs. We use the Casio book for keyboarding and sight reading.
I want to assure everyone that it is possible to take children who sing totally off-key and have them singing on key in fairly short order when you use a keyboard and just practice scales. After scales, have them learn 3rds (Do-Mi), fourths (Do-Fa) and fifths (Do-So). That way they'll be able to sight-sing from written music.
We are working through the fine arts section of Hirsch with the worksheets. Each time we encounter a new composer we visit the internet music site and listen to his (so far no "her") music and discuss how we can tell that it is the composer's style.
In the art section we visit the internet museums and view the pictures in color. Whenever possible, we do a search for the various buildings that Hirsch discusses and view photos of them too.Resources: