Really interesting thread!
I'm not a teacher, but I do meet a lot of music & non-music teachers in my day-to-day work (plus I have 2 young children of my own), and I frequently come across the confidence issues discussed, the perception of music as difficult and the trouble in making music something that can be included across the curriculum, whilst keeping it fun for the whole class. Above all, I'd say the most common phrase I hear coming out of non-music teachers mouths is : "I haven't got a musical bone in my body"
That phrase always irks me because we all, I think, know that isn't really true. We all sing in the shower, or (in the UK, especially) when we think nobody else can hear us.
We all have "musical bones" - we are born with them, and they are essential for all of our speech and language development. We use exactly the same parts of our brain for listening to and processing our mothers voices from day one, as we do for listening to and processing music. (For more on the academic research behind this, watch this excellent TEDx talk by Anita Collins - "What if every child had access to music education from birth?"
I cannot agree more with teachingmusicquestion's statement that "I have never yet met a child who is not musical". For me, for anybody to have lost their musical bones by the time they reach early adulthood (I think age 16 is around the threshold where people either have or have not decided that they want to play an instrument), is an indication that something is going badly wrong in the way music is traditionally taught up to that point.
Early music education should be playful, unreserved, and most of all fun. With so many teachers believing that they have lost their musical mojo, why not let the children (who still have a firm grasp on their own mojos) lead the teacher, and just let them play? The formal stuff can come later.