Sticking to hearing, 85dB is normally taken as the level that causes permanent damage but many of my ENT colleagues think it is lower - 80 - and as this is a log scale that is of concern. Hearing loss in children is often missed resulting in educational and developmental issues, and normal reduced acuity later in life from osicular sclerosis will be accumulative condemning them to significant disability and increased risk of dementia. I really would not fly a child until they are old enough to fit and wear good quality headsets.