Thanks for your comments, Dak. Yes, definitely a good idea to fit the helmet correctly!
A helmet could save your child's life, but it's pretty improbable. That 85% research claim is misleading and probably came from the study mentioned in http://www. cyclehelmets.org /1131.html - if you do decide to curse your child with a heavy helmet to balance on their head while they themselves are still learning to balance on a bike, please make sure it is fitted correctly and tightly, so at least you aren't placing them at unnecessary risk of strangulation or concussion. The most important thing is to teach them to watch the road and spot potential dangers so they can avoid trouble: a helmet will make little difference if they are hit by a larger vehicle.