My daughter (3) has been breaking out in clusters of hot hives for 3 days. only possible pattern... cooked tomatoes. could this be a possible food allergy?

Yes: A food allergy is possible. I would recommend avoiding the suspected food and see if the hives resolve.

Yes: Food reactions vary from very mild to major.Kids can have their lips & face swell with intake of some foods, or develop blotchy rashes & hives.Some just have excess nasal secretions. Once triggered, hives may continue to come out for 3-5 days as the protein in the product is broken down in the body and passes through the intestines.