The term used for any vampires Notte created himself.
These Night Children are special because they are the closest to Notte in terms of powers and abilities, including immunity to sunlight. Notte doesn’t make many children; history has proven how few people can truly handle that kind of power, and giving it to the wrong people is amistake he doesn’t intend to make again.
So why, you ask, did he make Marshall?
An excellent question. Might be a story there.