If your not supposed to give children's aspirin to kids, then why do they still make it and sell it?

Still a good med. As with many medications, we discover over time that some complications require avoidance or close monitoring. A dramatically good acne med can cause liver injury if its not monitored or birth defects in a pregnant woman but it works well. A drug that causes birth defects is used with some patients to keep their cancer from recurring. Having important benefits is why some dangerous meds are made.
Other uses-low dose. It is called low dose Aspirin and it has other uses, including protection against heart attack and stroke.
Actually... I don't think they even call it "children's aspirin" anymore. It's called "low dose" Aspirin now and it's very popular for preventing heart disease.