Brands and Experts suggest replacing your helmet at least every 3-5 Years regardless of use, crashes or visible wear. This is due to often invisible material wear within the helmet potentially jepardizing your protection.
You should also replace your helmet with any major impact. Especially impacts large enough to leave a dent or scratch to the outer surface.
Kids helmets are especially prone to being dropped and may be of compromised safety if they are dropped from a moderate height, like a table. Its for this reason we recommend Hardshell helmets for kids as they are more resistant to damage, though still need to be replaced with age or visible damage.