[LAU] Music for the deaf

My sister is a specialist teacher for hearing-impaired primary school children. As part of her curriculum she includes music and in particular, nursery rhymes etc for the younger children. She would like them to be able to sing these at home with and/or for their parents. For those children with non-hearing-impaired parents, this is not a problem but many of the children also have hearing-impaired parents. Therefore she would like to produce a CD of her singing for the children to take home and use. I would really appreciate any help members can give me as I am not a professional musician or recording engineer. 1) She will be singing unaccompanied (she is a trained singer and is perfectly competent to do this) in an alto register to avoid any distraction for the children from accompaniments etc. Does anyone have any suggestions about this? (eg effects for recording, effects for the headphone mix etc) 2) This one's a bit more specialist so you may not be able to help - hearing impairment often starts with loss of high frequency response. The obvious thing would seem to be to boost these but I don't know if that would be correct. Does anyone know? Any comments on any other aspects of this project would also be more than welcome. Hopeful regards, Simon