I would be checking out the preservatives and additives. All of my kids have had reactions to certain preservatives and additives in food. Angelica worst of all. She could eat some types/brands of foods but not others. ie, she can eat Heinz tomatoe sauce, but cannot touch any of the other brands (especially the cheaper ones), because they use different preservatives and additives. Nate would always throw up cows milk once he started drinking it in a bottle (at about 15months, was b/f before that), we had so many issues with his health because of it and had to put him on toddler formula (because he didn't react to it and it contained more iron and other vitimins and minerals he was deficent in). Bazza has occaisional reactions to milk, we have him on Lite milk now he is nearly two and has more then enough other dairy, which is slightly better in that he's reactions are less common (but he drinks more). There is another milk "A2" which is great as it is completely preservative and additive free, but we cannot always get it, and it is much more expensive. Similar stories for different yogurts and cheeses and other foods. Even breads have caused us issues at times. My kids are always at ther healthiest when all their food is fresh and preservative free - the only thing that stops this being the case all the time is the cost - but we still try to ensure the bulk of their food is that healthier stuff most of the time.

Also if you kids have a reaction to something, it doesn't alway mean they will have a reaction. With the tomato sauce, because we try to avoid the other brands as much as possible (which is an interesting concept when eating out at places like Macca's or Lollipops), we find that when she does have the other brands 'occaisionally' now she is fine - but if she tries them too often the reactions come back (big red welts around her mouth and face).