I have a friend who feeds their child a raw fruitarian diet, they feed the child only raw fruit (a mixed of various fruits) and different type of nuts. The child is quite small for their age, but they explain this as one of them was very small as a child and that the child takes after that parent. The child was fed this diet from birth and he was breastfed until around 3 years old. Apart from being small, the child seems to be developing fine, in speech etc..
Is this considered child abuse? I have tried to talk to my friend, but they do not even want to engage in the subject, they do believe that this diet is the best and they (the adults) mainly follow it too, which a few exceptions here and there (as in they will rarely have some cooked food). Is there anything I can do or should I stay out of it?