Hi Ousaima,
all examples I gave are general possibilities that have in some cases been encountered. I'm not saying that any of these do necessarily apply for your kids. The more details you know, the more you can rule out or confirm.
1. The point of age, as it is similar for both children, can be of significance, and even transferred from their ancestors. What disgustful thing happened for someone in your family at that age, that involved fresh fruit or sweets? The kids don't need to consciously know that.
2. As the phobia isn't only about the real thing but also about a package, I should say there is a "new brain" issue going on with imagery involved. I wonder: is there a story they were told, or watched on TV, where somebody was poisoned or enchanted with a gift of sweets?
3. Under which circumstances does your son lose his voice after eating meat, under which not?

For 1. and 2., if no ideas show up, and it's important to understand, one can do a regression process or work with kinesiology to find out the answer.