No, probably not. Unless you had a sap-glove on the hand you slapped the li'l bastidge with.
Most folks have never dealt with humans that are outside the envelope of normalcy; People are generally 'nice,' well-behaved, relatively well-adjusted and non-violent, and used to dealing with people equally 'nice.' They just cannot BELIEVE that some kid is just plain BAD. To quote any mass murderer's neighbor: "He was a GOOD boy, loved his mother, always quiet, stayed to himself, I just can't BELIEVE he would disembowel a busload of. . ."
Those of us (un)lucky enough to see people at their worst tend to be a tad more jaded in just what people are capable of doing to themselves or others. One of the things we do see from time to time are the little darlings whose mothers should've sat upon them at the moment of birth; These little monsters will NOT be 'fixed', as there is just something WRONG with their 'wiring.' They'll just grow up to be bigger monsters. Many examples exist, from Hitler to the delightful kiddies of Columbine or the rotten bastidge from Brazil this week.
As the average person isn't equipped mentally or physically to really deal with a truly BAD kid, yes, you DO have to call the cops on an 8-year-old from time to time. And the cops fully expect that no matter what they do, some 'nice' person will find fault with it as they just can't put necessary force into context.