child cravings

Hello!
To begin, I believe that children know what and how much they should eat to be healthy. My ds, 3 1/2, eats more than I do every day and is not overweight but keeps getting taller and taller. We are mostly vegetarian/vegan, but being poor, sometimes accept food that falls out of this category. We eat lots of fruit and vegetables but less and less tofu/soy products in the last few weeks (money). When I know ds has eaten and eaten but still says, "mom, I'm hungry" I ask what it is he would like to eat. Sometimes it's something sweet he's looking for having, even though there are no sweets in our house. What I am really concerned about is his craving for salt. I believe that certain cravings mean certain difficiencies in diet (though I believe that my chocolate craving on the first day of menstruation aids the cramping be less severe). Does anyone out there have any information on what craving salt (salty rice crakers or corn on the cob with salt) indicates? I do know that it is the salt specifically he craves because he tells me (and he is very aware of his bodily needs). Should I look into giving ds only Celtic Sea Salt?
In addition, I would love to know if anyone has information on why the craving for chocolate is linked to menstruating and lessening cramping? What does the chocolate do for my body?