goodies! Soon the parents will be wondering why the child displays certain behaviours at certain times and places, ignorant of the child's real motives for their behaviour.
It is unkind because it will start to condition the child into a life of fluctuating mindsets between that of self deprivation ("when I have been naughty") and self spoiling ("when I've been good"). This is the beginning of "mood eating", a topic which his covered in detail in Chapter 8 - "Food the Mind and the Feelings" on page 546.
Whether it be quality food or junk food, food should be understood right from the beginning as something we need to live,
something we enjoy at meals times, and something not be misused to satisfy emotional hang ups. It should never be seen by children as tool of power by the parents, doled out in reward because "you were so good sitting quietly in the dentist's waiting room for an hour without mucking up" or withheld in a bribe such as "if you don't stop doing that I won't buy you an icecream".
A child growing up with these patterns of food appreciation will very soon find ways of bypassing their parents' food games, helping themself in secret to food in order to exercise their power over food, and they will probably grow up without any respect for food or self discipline in their eating habits.