Helmets sold in CoBR bike shops will be tested to certain standards. The best test is the Snell Foundation test. Other tests of note include ANSI (US) and BS (British).
When kids fall off............it is quite often their head which hits the ground first. You'll therefore be pleased to know that cycle helmets are really at their most effective at slow speeds.
Always make sure your child likes their helmet, it really shouldn't matter what you think about it. Providing it meets the necessary safety standards, let them choose it. Remember, you want them to wear it rather than remove it once you're out of sight.
At the risk of being accused of scare mongering; what can happen if you don't wear a helmet.