Aha, a nice trick for manipulating your kid: use threats small enough that he rationalizes his compliance by changing his desires: The Forbidden Toy.
If a person is induced to cease performing a desired action through the threat of punishment, he will experience dissonance. His cognition that he is not performing the action is dissonant with his cognition that the action is desirable. An effective way of reducing dissonance is by derogating the action. The greater the threat of punishment the less the dissonance—since a severe threat is consonant with ceasing to perform the action. Thus, the milder the threat, the greater will be a person's tendency to derogate the action. In a laboratory experiment 22 preschool children stopped playing with a desired toy in the face of either a mild or severe threat of punishment. The mild threat led to more derogation of the toy than the severe threat. (PsycINFO Database Record (c) 2012 APA, all rights reserved)