dear Mignon,
How old is the infant?
In the case of very young babies, I prefer the parent to a "ball". By holding the child and moving in all directions, (at various speeds, with the appropriate support of head, or shoulders and trunk only, depending on the possibilities) you are giving the child a lot of sensory information.
In the case of the small infants, a swiss ball can be used, as a fun way of learning how to shift weight (which is needed to be able to move at all). But also doing some weight shifting in functional positions would be my choice.
Change situations and positions a lot = morer fun for the child and stimulates more.
good luck
esther de ru