In the present article, a view of children's emotional development is articulated that is consistent with, and which seems necessary to supplement, current neo-Piagetian theories of intellectual development. The basic assumption is that cognition and emotion are generated by different systems, each of which is necessary to normal functioning, and which together produce the structures that are characteristic of normal human development. On the basis of this assumption, it is hypothesized that any change in one system will have a concomitant or subsequent effect on the other. In particular, it is hypothesized that the arrival at a new cognitive-developmental stage will influence (A1) the types of emotions children are likely to experience, (A2) the types of situations in which they are likely to display these emotions, and (A3) the nature of the control structures they can develop for dealing with these situations and/or the emotions they elicit. At the same time, and reciprocally, it is hypothesized that exposure to certain specifiable emotional situations will have the potential to influence (B1) the amount of time children spend in epistemic activity, and hence their rate and terminal level of cognitive development, (B2) the particular directions in which they channel their epistemic activity, and hence their cognitive-developmental profile or their cognitive style, and (B3) the efficiency of their basic cognitive processes, either general or specific. The paper concludes with three preliminary tests of these hypotheses. The first study tests hypotheses A1 and A2 by examining the emotional responses of children at different cognitive stages to a situation where their mother ignores them for another child (either a newborn baby or a peer). The second study tests the same two hypotheses longitudinally, by examining infants' emotional reactions to a brief separation from their mother as they approach and then pass into a new stage of cognitive development. Finally, the third study tests hypotheses B2 and B3, by assessing the cognitive development of children who are either emotionally disturbed or normal, and who either have or have not experienced the death of a loved one at an early age.