Don't notice things in their peripheral vision as readily.
Can't judge car speeds.
May have difficulty working where a sound is originating.
More likely to imitate inappropriate behaviour.
Can't see over bushes or parked cars.
Can't be seen behind bushes or parked cars.
Have a short concentration span.
Tend to be very active and are less likely to stop at the kerb and more likely to dart into traffic.
HOLD THEIR HAND NEAR TRAFFIC. In one accident study, about half of injured pre-school children were injured running away from, ahead of, behind, or across to another person, often a parent.
Help them to choose safe places to play.
Explain to them how to cross the road at the times you do it with them.
Set a good example. Be mindful that they are not as capable of doing some things that are safe for adults.
Don't let them ride a bike in or near traffic.
Describe traffic in terms of "fast", "slow", "near", and far.
Point out and explain signs, traffic lights, safe places to cross the road, curves and bushes that may obscure their view, and dangerous places in your area.
Teach them to look and listen for traffic and think about what they are doing.
Take them to school on the safest footpaths.
Use safe crossing places so that they will copy.
Don't let them drive their bike in any place outside a park, playground or schoolyard unless accompanied by an adult. Ensure they always wear a helmet.
Tell them about road laws that relate to safety.
Talk about safe places to ride a bike. Ensure that they always wear a helmet.
Try to get them to wear conspicuous colours.
See also http://www.lib.mq.edu.au/curric/road_safety_biblio.htm