MS Access 2002 – Building a Primary Key

I’m new at using MS Access. I’ve gone to the Fred Pryor Workshops – Beginning and Advanced, and I bought the MS Access 2002 Bible. According to the Bible, it can be done, but I’m having trouble understanding the details of how to create the Primary Key that I want.
I’m working with a db that has a table of Family names using FamilyID as Primary Key and need to link it to another table that contains a list of all the children in that family. I’d like the primary key in the children’s table to be FamilyID, a hyphen, and a 2-digit sequential number.