Heat exhaustion happens. Sprained ankles happen. Fainting b/c you lock your knees happens. Torn ACLs happen. This is military training. No matter how safe and secure the military tries to make the training environment -- and they do try -- some people will get hurt and/or sick. It just happens.
I know you're concerned about your child. However, the fact that a couple of plebes had heat exhaustion doesn't mean USNA doesn't care about the plebes. That's akin to saying that, if you as a parent let your kid play soccer and he/she tears an ACL in so doing, you don't care about your child.
In this case, USNA can tell mids to hydrate but can't shove water down their throats. And, some people simply acclimatize differently. If the military stopped training because there was some remote possibility that someone might have a medical issue, there never would be any training.
Remember, your child is in the military. The military will take care of him/her. But that doesn't mean that your child will get through the rest of his/her life in the military w/o a scratch. The good news is that plebes are monitored very closely and, if there is a problem, will get immediate and excellent medical attention.
I'm beginning to think that the internet and immediate info on everything isn't such a good idea as it causes people to worry unnecessarily.