I’ve always understood the rule of thumb being 1/2 the length of the marraige for Alimony, but in the case of special needs children, is there any limitation to duration.
From the primary caregiver, I assume they want indefinite potential for alimony, due to the uncertainty of care needed, and due to the implications it may have on their employability. They would expect the other party to support the child for as long as needed.
From the paying parent, I would assume they want to have some boundries on how long that the payments could go on, so they are not held to a life of servitude. They would expect at some time that the primary caregiver would find a way to support themselves and the child.
For this case, think of a child who has an unpredictable future. May be out of school more than others, definitely would need and IEP in school, and could have hospitalizations one or many times a year, lasting from a few days to a several weeks, each. At what age would the child be considered “self-sufficient”, such that the parents would not be required to be there 24/7 for hospitalization?