Children with expressive language disorder have difficulty conveying or expressing information in speech, writing, sign language or gesture. (For preschool children, the difficulty expressing themselves in writing is not evident, as they have not started formal education.)
Rectangles have longer sides than any type of square. Opposite sides of rectangles are of equal lengths. All sides of squares are of equal lengths. Rectangles have longer sides than any type of square. Opposite sides of rectangles are of equal lengths. All sides of squares are of equal lengths.
So a square IS still a rectangle (still has four right angles!). Both are also parallelograms. One way to see that this is useful, is to realize that any special properties from the larger class: e.g. diagonals bisect in a parallelogram) still apply to the special cases (e.g. a square or a rectangle).