Broadly speaking, it can be conceptualised as coping, sometimes interaction with others, with some environmental challenge, often involving objects, and sometimes in conjunction with others, with an end point in view. Problem solving has two associated features. One is problem finding involving insights into what is missing in terms of arriving at a solution and requiring creativity. The other is problem shaping: revising the nature of problem so that a solution can be achieved. One enlightened suggestion for examining problem solving in infants is to couch it in term of the development of tool use.
See Ages and Stages Questionnaire (ASQ), Balance scale task, Cognition, Cognitive science, Coping, Creativity, Crystallized intelligence, Delphi method, Executive function (EF), Fluid intelligence, Flynn effect, Heuristic, Logical reasoning, Microgenetic method, Reasoning (psychology), Scaffolding, Tower test