In the USA there are around 10,000 people who die from ATV accidents.
Some of those people are kids and some are adults.
A lot of those ATV accidents could likely be prevented but sometimes they may not.
ATV's are dangerous when used the wrong way or if you speed on them or run them down highways which you should not do.
But as long as you wear your helmet and other safety gear for the ATV and ride the ATV correctly and do not speed and be aware of your surroundings then the ATV is pretty safe.
More people ride the ATV safely than they do die.
Even cars can be dangerous and many people get killed in cars.
Little kids should never ride ATV's and when they are old enough to ride the ATV they should ride an ATV that is made for their size.
And you should always supervise them.