In my opinion even though your sons hr didn't go above 100, it sounds like it could be POTS. It did go up 30 bpm. Do you know what his vitals were when he vomited? Not knowing your Daughters vitals it would be hard to tell, but I'm guessing your intuison tells you what's going on. Listen to it. My first TTT was nagative. It took 2 years before I finally got diagnosed. I knew all along this is what was wrong with me. However the Dr I had didn't understand POTS. He himself admitted as much. Maybe you'll need a second opinion, I would ask for copies of the TTT and take it to another Dr. Best luck to you and your little ones. (((HUGS)))