what you have to ask yourself:
would you make your 8 year old daughter wear a helmet if she had to cycle 5 miles everyday to school and back?
I would be far, far more concerned that she was properly trained and confident in riding on the roads with traffic than anything else. I wouldn't stop her from wearing a helmet if she wanted to, but I wouldn't force it on her either.
I dont wear crimpelene and lycra, but a helmet and a high viz jacket are essential
Again, I'm far more concerned with active lighting (when needed) than hi-vis clothing. Even the brightest hi-vis jacket won't show up at all with the sun low in the sky in the eyes of drivers.