Hi.. Can understand your concern.. As per your query it is correct that if any painful dental procedure is to be carried out in a child then a dentist has to give him an anesthesia injection otherwise he cannot carry out dental treatment as a 4 years old child cannot cooperate in his or her treatment in pain and on the other hand it is also unethical practice to work without anesthesia where it is indicated.. If you are worried about anesthesia as your child is just 4 years then you need not to worry as there are fixed quantities in which anesthesia is given to children depending on their age so that it does not harm them... On the other hand the dentist always applies an anesthesia gel or spray over the area where anesthesia injection is given so that the upper most layer of mucosa (skin inside mouth) gets numb and does not cause pain in needle prick and the child does not get anxious.. Hope you get your query solved. Thanks..