AS/NZS 2063 Bike helmets sold in Australia have been
tested to the Standard AS/NZS2063. These are the helmets legally required for use on bike. Hard shell, usually lots of ventilation holes, polyurethane foam inner and padding

THE FIT you want the helmet to be comfortable on the head and not move forward/backwards or side to side.  These Three lines – Helmet should fit snugly ‘across the eyebrows’ ‘down the sides’ and ‘under the chin’.

ADJUSTING SYSTEM This allows the helmet to be tightened under the back of the head, at the occipital bone at the base of the skull.

AVOID helmets that have crazy features such as spikes, ears etc  – They are very unbalanced (imagine trying to learn to balance on a bike with something wobbling on your head). I’ve never encountered one that fits or stays still on a child’s head.

Be aware the difference of ‘skate’ helmets

SKATER STYLE helmets are those that look like a Skate helmet (bucket style) but have the bike helmet rating AS/NZS 2063. Hard shell, a few ventilation holes, polyurethane foam inner and padding

A SKATE helmet has a hard plastic shell as the outer that appears to be identical to that of a bike helmet; it is on the inside that the 2 differ. The Skate helmet has a hard shell but only has a soft foam cushion whereas the bike helmet has the polyurethane foam which is what is designed to compress when an impact occurs.

Many families buy their children the ‘coolest looking’ helmet, and from the outside the 2 helmets look identical, but it’s what’s on the inside that is going to protect them in a fall and an impact with either the ground or a vehicle.

(Edit June 2018: Thanks to @kerno_skunkwerx for correcting a detail on this page.)