I've done public fly tying presentations at a number of our state parks. I have a sign explaining small children may have problems tying the wooly bugger but, the parents insist on sitting four and five year olds at the table. They become perturbed when it doesn't look like the samples... Eight might be old enough but keep each group small so you can help a much as necessary. (Be prepared to tie many of them when the children become particularly frustrated.) It is fun to watch them try and when the walk away with a treasured souvenir. I wonder how many of us first got our interest piqued at a public fly tying demonstration?