The width and height of an element can be changed using the Bootstrap utility classes. These classes include:
w-{25|50|75|100|auto} the percentage width of the parent.h-{25|50|75|100|auto} the percentage height of the parent.
The available percentage widths are defined in the Bootstrap Variables file.
Bootstrap does not currently support using breakpoints for sizing the child elements however it is possible to write your own using Media Breakpoint Mixins.