Buying a bicycle helmet is not a mean feat these days as the
selection takes over a 20' wall space in the average bicycle parts
and repair shop. With all this selection it is hard to know what
is the right choice.
Go for quality first as you only may get one chance to test its
protective features. Look for certification labels on any and
all bicycle helmets before you even think about a purchase.
Sizing and fitting are equally important especially for infant/toddler
bicycle helmets. If you look around your neighbourhood, I'd bet
90% of the child's bicycle helmets are hanging to the back of
their heads. For a frontal over the handle bar fall this is going
to do little to protect their vital organs.
Be aware that many, especially lower valued bicycle helmets are
made of high density foam of one sort or another. Think of your
camping cooler. If a bicycle helmet gets left on the dash of a
closed car, the intense heat can deteriote the foam so be aware
of some of the issue related to care and inspection of your helmet.
As you're headed out the door on holidays it's also not a bad
idea to do a search on bicycle helmet laws in your area of travel
if you are hauling your bicycles.
You can't go wrong checking out two of the largers manufacturers:
Bell Bicycle Helmets
and Giro Sports.