Quality of materials: good materials and workmanship, strength, absence of danger.
Aesthetic quality: naturally without aestheticism, simplicity.
Educative potential: it has to fit the needs of children and their stage of development, leaving an open door to their imagination. You should also note that it should stimulate normal development of the body and promote manual or muscular dexterity, apart from encouraging the development of organs and senses, and it should also inspire creative thought and action, awake and encourage aesthetic feelings, sociability and make the child feel interested in the world around.
(El disseny i el nen. Les joguines. Barcelona: BCD, 1978)