I see people individually, as a couple, and as a family. I've counseled people of all ages: from 4 - 100. When seeing younger children and teenagers, I usually ask the parents to sit in on the session unless clients wish to be seen alone.
I am willing to mix and match depending on the agenda. Sometimes people like to split a session and I will see part of the family, or one of the partners for part of the session, and the other family members or other partner for the other part of the session.