Try to find out what their parents call hazards e.g. danger, nasty, bad, 'NO dont do that', etc as the language that the children use and know is the one to use at your event

Also note that children under 10 [I think that it is 10 - Please correct me colleagues if I am wrong] are not generally seen as being able to understand the concept so make it a game noting that the policy now is to introduce risk acceptance as against avoidance and that a childs biggest risk is crossing the road - just look at the death rates

Best of luck and enjoy the event