I just joined celiac.com expressly to answer your post!!
When I was 5-years old, I too complained of a "hot tummy" to my parents. They were never able to get a better description from me, and frankly, at this point, I have no recollection of how a hot stomach feels.
It was my mom, not the doctors, who first suspected celiac disease. This was the mid-seventies and there were ABSOLUTELY NO gluten-free foods that tasted good (or at least, none that my mom we willing to buy or try). I remember not being able to eat any treats or goodies for 6 months. My mom tried to reintroduce gluten on my birthday and gave me birthday cake, but I immediately regressed and started to complain of a hot stomach again. Six months later, she tried again, and I was able to eat gluten and have been eating it ever since. (About 10 years ago, I had my blood tested and an endoscopy, and there were apparently no signs of celiac disease; just a high IgG). I really don't get it, because my symptoms were so extreme at age 5.
I now have a 5-year old daughter, and she seemed to be developing the same symptoms I had and so we took her off gluten. A couple of months later, she started developing similar symptoms even without gluten - cramping and diarrhea -- and we found out she is lactose intolerant. After taking her off lactose, she seemed much better, so we reintroduced gluten. There were no dramatic consequences, but about a week later, she started complain of a "hot tummy" and started to have diarrhea again (no cramping this time).
Our gatroenterologist told us to wait a couple of months while she keeps eating gluten, and then they'll try the blood panel and if necessary, the endoscopy.
(I have to admit that when I was eating gluten-free with her, my stomach felt better as well)
Oh, and the dr. had never heard of the hot stomach symptom!