Baby spells are spells which effect unborn children. That is, spells which effect conception or spells which will effect the child as it grows in the womb.
These spells are not reversible unless there are instructions for the specific spell on how to reverse or cancel it.
Great care should be taken before casting these spells. As the child born will under the influence of magic since birth, they will have a much higher tolerance and a much higher control of magic as they grow.
It is often the case that a child born of magic will ultimately destroy his creator by the same means.