Can someone please answer my question.

Why is it called the brown stair instead of broad stair in most schools nowadays?

While working with the brown stair, why is word "thick" used instead of "broad"

When the pink tower and brown stair are kept next to each other, what do I discover about the height?

Thank You

Children in this age group are interested in "what". So we give names. Why thick and why not broad? i would say give both but second name, a little later(synonyms). First name depends on the common usage.