In reply to tiffanykate12:
I have always worn a helmet as an instructor outside, and if their are children around, I will wear one during personal climbing. It's all about the example we set. Only certain sites where I have worked required helmets to be worn indoors.
Indoors, I think it comes down to how developed children's awareness is, whether they should be responsible for their own safety yet (maturity) and whether they are as impact resistant as us adults. Children don't bounce back as easily, they are also more likely to do dangerous things initially and don't yet understand the consequences of certain actions (being told often isn't enough). However, there are times where a helmet indoor would be more dangerous, on auto belays for example, where a helmet lip can catch on holds on descent and lead to asphyxiation.
I think the discomfort factor for instructors can be frustrating if you are wearing it all day. I objected to wearing a webbing harness (had to match the children) as I was in it for 6 hours, not 60 minutes and spent a lot of time hanging around. The employer were not willing to move on this, or many other issues of staff welfare, so I left that job. Some employers have been more supportive and allowed use of own, or provided more comfortable equipment for instructors.
A little digression however I now know about four individual people who's lives have been saved by helmet:
1. Gear ripped on a gritstone route, hit head on rock on landing. Helmet was obliterated. Could have been their skull.
2. During a wall reset indoors (closed area) a very large volume fell about 16m and hit a member or staff below (wearing a helmet of course). Knocked them clean over and made them very dizzy. Helmet was obliterated again.
3. Fell 16 meters from top of a crag. Hit the deck and ended up in a coma for the best part of two weeks. As I understand it, the doctors said that, without their helmet, they would have died.
4. A cyclist friend was knocked off his bicycle and head butted the curb. Cuts and scrape and a great big polystyrene jigsaw to show for it. He's okay and cycles every day.
All these people were adults.