Come-and-go Children

I had an idea for a fantasy land, in which Sanfilippo Syndrome is very common and affected people are worshipped. Now, if I can think of a plot, I may end up writing a story about it. But in the meantime, here's a description of how they are viewed in this society (if you think up a plot, feel free to let me know):

They were called come-and-go children, or holy children. They were so holy that they could not live long. They started out just like everyone else, but they were destined for holiness. Shortly after they started walking and talking, the first signs of holiness would appear.They become very energetic, and need less sleep. They stop talking and their hearts open up to all kinds of people. Those are the first signs of a come-and-go child.
Parents are delighted to see this in their child, because the child will be very holy. But they also know they will have less time with the child than usual, so they must make more of the time they have.It is common for parents of come-and-go children to stay home with their child often, letting others do the work they’d have done. They have more valuable work to do - care for their holy child. Siblings also care for the holy child, and both siblings are parents are elevated by this child.
Come-and-go children get less energy after awhile, and start tiring easily. Eventually, they can no longer walk. At this point, parents will sometimes resume work, but they take their child with them everywhere they go, riding in a sleigh. Other people cluster around the child, hoping to be blessed by this holy child. People ask the child to visit their fields or heal sick people.
Around the age most children enter adulthood, come-and-go children start weakening. Their holiness is too great for their body to bear. Their family stays with them at all times, taking turns to sleep or tend themselves so the holy child always has someone there. Others visit, and the parents interpret the child’s signals to decide who may enter and when they must leave.
The parents of such children often have many more, because it is known that parents and siblings of come-and-go children are very likely to produce more holy children. Many families try to arrange a marriage with the sibling of a come-and-go child.
Siblings of holy children often marry the siblings of other holy children. That way, the chance of having a come-and-go child is very high. Cousins and other relatives of come-and-go children are also more likely to have come-and-go children, and are also more easily married. I know of one woman who had a child outside of marriage. At first, she was shunned and the father of the child insisted she was not his child. But when that girl started becoming very energetic, and then stopped talking, he was proud to be her father, and the woman got many offers of marriage.
It can be hard to be a family without any come-and-go children. But it is especially hard to have a foreigner in your family, because foreigners never have come-and-go children. It is said that in other lands, come-and-go children are viewed as a tragedy, and parents of one never have another child for fear they, too, will be a come-and-go child. Siblings of those children often never marry. Because of that, come-and-go children are almost never born in foreign families. Many people think foreigners are either confused or simply evil, because they think it bad to have a come-and-go child.

Interesting how something can be viewed totally differently, right? A degenerative neurological disease becomes a condition in which they die of being incredibly holy. I thought up this world because I was wondering how dying in your teens from some kind of disability is considered a tragedy, but dying in your teens (by years) because you're a cat is sad but accepted.
Ettina