Gamete cells get a random half of all genes from each parent so there's about 2 unique possible 'sets' from each parent, and 2*2=4. However because it's random I think you can only say there are 4 distinct completely unique possibilities in theory, but it would be very unlikely for that to actually happen in practice.
Each parent supplies half the genetic material. But each sperm and each egg have a randomly different set of one half of each chromosomes.
So if you have 10 children chances are they each have a unique set of chromosomes.
