What should i do about my baby cousin?

My mother and I have both noticed that my three-year old cousin is showing major symptoms of being autistic. We both recognize them because my mom studied medicine, and my brother is autistic and showed the same symptoms she's showing at that age. Neither of us want to tell my aunt b/c she's already neglectful of her kids (e.g. has her relatives or friends take care of her kids the days their babysitter is off even if she's home, feeds the girls McD's on a daily basis, has delayed moving back in with her husband fr the past 1 1/2 years despite the fact her kids clearly need a fatherly figure around) and we don't know what she will do if we tell her. Though it's very likely she won't listen even if we tried, i still feel something should be done. it may not be my family or my business but i care about my cousin very much.