Ball pythons may get to four feet easily, but in reality, they are not powerful to a healthy person (hell, I might have rheumatoid arthritis real bad, but I can pull both my BPs off me if needed) or child who has good co-ordination (7 years and older is what I'm thinking).
There is a risk of salmonella with reptiles, but you can easily get over this by keeping their cage clean and washing your hands. All animals can bite, but BPs obviously don't very often, and when my male tagged me, it hurt because of how hard he hit, not because of the three little scratches and drop or two I bled; my corn snake of the same length has caused more damage with a bite, and a mouse put scars on my finger (they might be temporary, as those bites were only a month or so ago).
I personally think a cat or dog bite is more likely to become infected, as all the times I've been bitten, the wounds have gotten red and inflamed, same with when our cat had claws. The biggest problem I had with any snake bite was a small amount of blood.