As I read a particular section from the article referenced below, I was reminded of something that I observed over 20 years ago.  I thought it was a mistake then and know that it was now.  I was barely 20 years old and attending a local community college (studying child development).  For spending money,  I cared for a little girl - like a nanny. I was with her from age 9 mos to age 3.  We were very close. Yes, I looked after her during the time of two major milestones.  The establishment of food preferences and toileting.
   One day during her potty training, I remember arriving at the house and hearing that she had JUST "pooped" in the toilet.  She was rewarded for this big girl activity with an M&M cookie.  
   In the article I read today, the section on food preferences (p S53) notes that children do not really need to learn to like high fat/high sugar foods because there seems to be a universal preference -taste wise - for fat, sugar and salt.  They don't have to learn to like the taste, but their preferring foods that are high in fat and sugar is shaped by their experiences.
   When these tasty foods are paired with experiences that are also pleasant, children learn that they are special foods.  They think that the foods made them happy (instead of the people or situation)!  Obviously, the cookie story is an example of a food reward.  Other conditioning factors include celebrations and holidays which center around energy dense foods.  Seeing the people that you love (parents) eat these types of foods is also normative. The article offers this caution...
In situations where foods high in sugar, fat and salt serve as rewards, the functions of food can become confused.
Though I had considered all of the above I had not thought of this additional concern noted by the authors...
Foods eaten in order to obtain rewards can often become disliked.
   It took a long time for me to add spinach and mushrooms back into my diet.  I remember sitting at the table - the reward being leaving the table or dessert - but only after eating THAT food.  
    These things are  worth bearing in mind as a parent OR grandparent but also in considering your own food preferences.  
    Today's examples were on the individual level, but I assure you, the food industry is doing everything it can and spending billions to ensure that you prefer the foods that it sells.  Those foods are most often energy dense - high (sat) fat and sugar.   

Nestle, M., Wing, R., Birch, L., DiSogra, L., Drewnowski, A., Middleton, S., Economos, C. (1998). Behavioral and social influences on food choice. Nutrition Reviews, 56(5), 50-64.