The life cycle of a successful textbook reaches well past the life of its author, given that copyright law currently extends rights in a work to the life of the author + 70 years. That means not just your children, but even your grandchildren may benefit from the fruits of your labors. At the same time, for books—and in particular textbooks—governed by publishing contracts, it is important for both you and your heirs to understand your, and by extension their, rights and responsibilities.
The first step is to pull out your publishing contract. If it is a typical royalty-bearing contract, then you likely have rights in every revision in which you participate.