During the years of childhood, children's ideas evolve as
a result of experience and socialization into "commonsense"
views. For very young chiIdren (aged 4-61, air only
exists as a wind or a draft-young children do not conceptualize
air as a material substance. The notion of air as stuff
normally becomes part of children's models of the world
by age 7 or 8. This stuff is then conceptualized as occupying
space but as being weightless or even having negative
weight or upness (Brook et al., 1989). This example illustrates
a much more general point: that the entities, such as
air-as-stuff, that are taken as real by children, may be quite
different at different ages. In other words, children's everyday
ontological frameworks evolve with experience and
language use within a culture. This change corresponds
with what others describe as radical restructuring of children's
domain specific conceptions (see Carey, 1985; Vosniadou
& Brewer, 1992).