To add to the discussion about helmets (and changed name to post this as it would be quite revealing!) I was involved some years ago in a company which was the first ever to test helmets after an accident...
Helmet safety standards are roughly speaking the same for anything from ski to cycling to riding etc. The test involves putting a head form (metal lump of a certain weight) in the helmet and then dropping the helmet from a preset distance. The head form has a sensor inside and it measures the shock to the head form through the helmet...
The test requires one drop and the sensor must measure below a certain value (drop is from a number of feet up in the air (representing a person of e.g. 6 foot falling over)
we were the first ever company (and possibly still the only company) to do formalised testing on what level of impact in the first accident would mean that the helmet would no longer perform to standard in a second accident - i.e. what level of accident is needed to make the helmet useless afterwards...
the results were quite frankly shocking - if you are a rider who comes into the yard and takes off your helmet and drops it on the yard floor - throw it out / if you knock a bike helmet off a kitchen table onto a hard floor - throw it out / if your child is wearing a helmet on a scooter or bike and falls off - throw it out (helmet not child 
) - I would have to dig out the results to give precise figures, but basically any shock above a drop onto a carpet or equivalent could very easily damage the helmet enough to stop it working again in the future...
The way helmets work is simple - significant damage to the human is not from the impact or abrasion to the skull - it is in the skull stopping movement suddenly (i.e. impact with the ground) and the brain continuing to move - hitting itself against the skull on the inside - think of it as whiplash to the brain... a helmet works by using compressible polystyrene, in an impact this squashes, absorbing some of the impact, but critically it acts like a pillow in slowing down the de-acceleration, so rather than the skull coming to an abrupt stop and the brain hitting it inside, the skull continues to move at a slowing pace by compressing the skull into the polystyrene and slowing it all down - that is how it works...
The issue is that once compressed, the polystyrene will not work the same way in the future, it can crack, it can compress, it can dent - and all of it is usually hidden under the shell of the helmet, so the wearer doesn't know... This is why motorcyclists tend to really take care of their helmets - it is life or death for them... but children don't and while I don't want to overly worry people children who take the helmets off once having cycled to the playground / school / etc. and they get knocked onto the ground - well those helmets may be useless...
having said all that - any helmet which meets the relevant safety standard will have gone through the same testing - beyond that the price difference is all about style and brand and offers no extra safety... so any damage or accident, please replace the helmets...