I'm sure you'll be just fine. Anaheim has always been a major exception in SoCal as far as gangs and violence goes, and it is bound to see outbreaks every now and then. Just play it smart and you should be fine. The area around
Disneyland is super safe, so stick to that area, and you should be fine. All cities of this size have issues like this, and the only reason it's news in Anaheim is that it has been so freakishly rare in the past.
Have a great trip! I'm sure you'll have a fabulous time, and if you stay close to Disney property, you probably won't even notice that anything is different.