Algorithm Help

Here's my task: A group of kids is going to be staying with different host families throughout the next 8 months. The number of kids staying with a host family can range from 2 to 10. When deciding which kids should stay together at a host family, the idea is for the system to put together kids who have stayed with each other the least on past weekends. So, if a host family can keep 5 kids, then the group of 5 kids who have stayed together the least will be chosen. I can't think of an easy, quick way to accomplish this. I've tried various approaches that have resulted in a lot of coding and being very slow. My idea was to give each group of kids a score and the lowest score is the group that is selected. However, this approach wound of iterating through several arrays several times which was really slow. Does anyone have any ideas on this puzzle? Thanks! Floyd