Dr. Herman Schachter is Tommy, Hector, and Angelica's pediatrician. He was first mentioned in "Slumber Party" as Tommy's doctor who advised Stu to give Tommy his baby drops when he and Didi found him sick. While little is known about him, he seems to be a very friendly, calm and patient man. As seen in the "The Shot" Tommy and Hector try to leave the doctor's office, only to get lost and cause a lot of commotion. Oddly enough, Dr. Schachter isn't angry at Tommy or Hector for what they've done. When he realizes that Tommy's afraid of him, he tries to be as calm and friendly to him as he can be.
When he realizes Tommy's still nervous, he brings out a lollipop to show him that he's a good person. He most likely does the same thing for Hector, offering him a lollipop. Both Hector and Tommy handle getting a shot very well and enjoy even picking out a band-aid. However, even when Dr. Schachter offers Angelica a lollipop, it doesn't go well for her. As Dr. Schachter and Drew are walking out with a sobbing Angelica who screams for her mother.
When Drew asks if she'll be alright and asks if the shot hurt her, Dr. Schachter calmly assures Drew that she'll be fine and basically tells that some kids just handle their shots better than others.
You can find Herman Schachter gallery here.