mg sez "I am confused..did he have a younger brother? Sometimes I count six in the Jackson 5 and one seems younger or at least smaller than Michael."

Randy (Steven Randall Jackson) is Michael's younger brother. He is older than Janet, who is the youngest sibling. Both Randy and Janet made several "guest appearances" with the Jackson 5. Later, after Michael left the group to build his solo career, the band reformed in 1976 as "The Jacksons" and Randy joined the group; they signed with Epic Records. Randy co-wrote their hit "Shake Your Body (Down to the Ground)" with Michael. He also worked with Michael on Michael's solo recordings.

For reference, Wikipedia lists three generations of the Jackson family on this page.