Here are some basic descriptions of various concepts that are developmentally appropriate for preschoolers, in order of acquisition:
Spatial (Prepositions) in, on, under, off, out of, next to, beside, between, behind, in front, around
Directional up, down, first, middle, last
Quantity another, one, many, one, two, empty, a lot, one-to-one
Size big, little
Time soon, later, wait
Qualitative same, different, color, both
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Children tend to generalize their knowledge rather and may not fully realize that an object may have more than one attribute. For example, it is fairly common for a very young child to generalize that all animals with four legs are dogs. It is through their experiences in comparing different characteristics (shape of the face, length of the tail, places they are found), that they begin to discriminate between the four-legged creatures. I have found the best way to introduce a concept is to offer many, many opportunities to model and experience the concept. Also, introducing contrasting concepts seems to be the most effective. For example, it is much easier to develop the concept of "up" if you are also developing the concept of "down."