This is not as easy as 100% because there is danger in walking across your backyard patio, that doesn't mean your never going to go outside because there is some ridiculously small percent that there could be danger.
Ball pythons are on average too small to cause any serious injury to a child of that age. You still can't say 100% because there are some larger than average that could do slightly more damage by bite or even constriction. In general, they just are not the type of python you need to be extra careful with compared to some of the larger pythons that can potentially constrict humans to death.
There are the two less serious dangers that have already been mentioned, a bite and even less likely salmonella or some other type of bacteria/disease. I've been in the reptile hobby since I was a young child, over 30 years and have never actually witnessed or heard of anyone getting sick from their pet reptile. That doesn't mean it doesn't happen, it's just to show how incredibly rare it is. Now a bite happens now and then. Bp are less likely to bite than most snakes but it does happen. A snake as small as a bp, the bite rarely ever does any damage. Now this is where it gets tricky, there is a very small chance it could get infected or they could get bit in the eye or some other more sensitive area that could cause a more serious injury. The thing about this is, there is a chance of dying every time you get in a car, there is a chance of dying every time you swim, there is a chance of dying every time you get on a bike, it is impossible to have 100% safety and what a horrible life it would be for children to be so sheltered that they would miss out on all the wonderful joys of life because there is a 'chance' of being harmed.
A ball python poses such a small percent chance of danger that it certainly is not worth concerning oneself with. They still should be respected as any live animal should be and precautions like washing hands should be followed but other than that they are about one of the safest animals a child could handle. I personally let my 3yo and 6yo hold any of my ball pythons whenever they want as long as it's supervised for their safety but more so for the safety of the animal because they are more at risk then the child in this situation.
So I guess the answer is yes, there is a small chance a ball python could harm a young child, just as everything else in life.