Thank you for this, it was really helpful. In response to what I am doing to learning Japanese, I do know the sound system of Japanese and elongated vowels, as it is the first thing I taught my students. The previous Japanese teacher represented the sounds as a double 'oo' for the elongated sound you referred to.My keyboard doesn't have this particular accent, therefore when I type out activities for students I simply add the accent manually to the sounds.
I understand your concern regarding my Japanese qualifications, however I was put into this position as there was no other person available to teach it and since I also speak Farsi and Indonesian and therefore have a language training background, I was placed in the position to teach 7 year olds. I'm a classroom teacher, art-specialist trained, who now has to teach Japanese as well. Luckily I enjoy teaching and learning languages.
Thanks again for your help.