Is water a better choice than apple juice? Yes. Is it insane and cruel to give apple juice? No.
Apple juice does have a lot of sugar, but at least it is natural fruit based sugar (assuming 100% apple juice is given), which is not as bad as processed sugars or high fructose corn syrup. It’s probably not a good idea to give it “constantly”, but sometimes is fine.
I would argue that apple juice would be a good thing to give to a sick child (assuming it doesn’t bother his/her stomach), since sick kids often eat little, and the juice can provide extra energy and electrolytes.
One suggestion would be to mix the apple juice with water – this makes the juice less sugary and irritating.