From John Dewey‘s Democracy and Education, pp 205-206:

It is important not to confuse the psychological distinction between play and work with the economic distinction. Psychologically, the defining characteristic of play is not amusement nor aimlessness. It is the fact that the aim is thought of as more activity in the same line, without defining continuity of action in reference to results produced. Activities as they grow more complicated gain added meaning by greater attention to specific results achieved. Thus they pass gradually into work. Both are equally free and intrinsically motivated, apart from false economic conditions which tend to make play into idle excitement for the well to do, and work into uncongenial labor for the poor. Work is psychologically simply an activity which consciously includes regard for consequences as a part of itself; it becomes constrained labor when the consequences are outside of the activity as an end to which activity is merely a means. Work which remains permeated with the play attitude is art — in quality if not in conventional designation.

From Erik Erikson‘s Identity: Youth and Crisis, pp 164-165:

It is true, of course, that the adolescent, during the final stage of his identity formation, is apt to suffer more deeply than he ever did before or ever will again from a confusion of roles . . . Much of this apparent confusion thus must be considered social play — the true genetic successor of childhood play. Similarly, the adolescent’s ego development demands and permits playful, if daring, experimentation in fantasy and introspection . . . Whether or not a given adolescent’s newly acquired capacities are drawn back into infantile conflict depends to a significant extent on the quality of the opportunities and rewards available to him in his peer clique as well as on the more formal ways in which society at large invites a transition from social play to work experimentation and from rituals of transit to final commitments, all of which must be based on an implicit mutual contract between the individual and society.

From Cindi Katz‘s Growing Up Global: Economic Restructuring and Children’s Everyday Lives, pp 96:

Each of these phenomena individually and collectively changed the everyday lives of children in Howa, impinging on the relationship between work and play in ways that anticipated and seemed to reinforce the stricter deviations between work and leaser time that characterized industrial capitalism. Under these conditions, work is valorized while play is trivialized as something done only in childhood or in time off from work. But the relationship between work and play is more vibrant and fertile than that, and in Howa its potency was still apparent . . . For one, children’s playful activities, like play almost everywhere, remained a psychological reservoir, an oasis for imagining things and themselves differently, for experimenting with various social and cultural relations, and for exercising what Walter Benjamin (1978a) called the mimetic faculty, where, in the acts of seeing resemblances and creating similarities, the power of making something utterly new lies coiled.

From Kurt Lewin‘s A Dynamic Theory of Personality, pp 105:

The fundamental dynamic property of play is that it has to do with events which belong in one respect to the level of reality, namely, in so far as they are activities to other persons (e.g., as against daydreams). But at the same time play behavior is much less bound by the laws of reality than is nonplay behavior: both the goal setting and the execution are in much greater degree subject to the pleasure of the person . . . The play field is hence a region more or less limited as regards reality which shows even in its content a most immediate relation to the unreality of air castles and wish ideals.

From Jean Piaget‘s Play, Dreams, and Imitation in Childhood, pp 147-150:

[Play] is determined by a certain orientation of the behavior, or by a general “pole” of the activity, each particular action being characterized by its greater or less proximity to the pole and by the kind of equilibrium between the polarized tendencies . . . play is distinguishable by a modification, varying in degree, of the conditions of equilibrium between reality and the ego. We can therefore say that if adapted activity and thought constitute an equilibrium between assimilation and accommodation, play begins as soon as there is predominance of assimilation . . . Since all thought involves assimilation, and ludic assimilation is only distinctive in that it subordinates accommodation instead of being in equilibrium with it, play is to be conceived as being both related to adapted thought by a continuous sequence of intermediaries, and bound up with thought as a whole, of which it is only one pole, more or less differentiated.

From the Playgroup UK Ltd‘s Role of Play in Engaging the Youth Market:

From Article 31 of the U.N.‘s Convention on the Rights of the Child:

1. States Parties recognize the right of the child to rest and leisure, to engage in play and recreational activities appropriate to the age of the child and to participate freely in cultural life and the arts.
2. States Parties shall respect and promote the right of the child to participate fully in cultural and artistic life and shall encourage the provision of appropriate and equal opportunities for cultural, artistic, recreational and leisure activity.

From Lev Vygotsky‘s Mind and Society, pp 102-104:

Though the play-development relationship can be compared to the instruction-development relationship, play provides a much wider background for changes in needs and consciousness . . . For the school child, play becomes a more limited form of activity, predominantly of the athletic type, which fills a specific role in the school child’s development but lacks the significance of play for the preschooler. At school age play does not die away but permeates the attitude towards reality. It has its own inner continuation in school instruction and work (compulsory activity based on rules). It is the essence of play that a new relation is created between the field of meaning and the visual field – that is, between situations in thought and real situations.