You might call them a Midwest variation of the Trapp Family Singers. Except that this family is into brass - a band featuring trombones, saxophones, and trumpets. And when the older children make it back from college and the younger ones are allowed to stay up late enough to be in a performance, they outnumber the Trapps by about two to one. The Wolves, or the Wolff Family Band as some call them, number 19 when they turn out in force.
When they practice in the kitchen of their white ranch house here, they move the two meal tables to the sides for an aisle and quickly assemble their music stands and instruments in the center. With a ''one-two-three-four'' from mother Nancy at the piano, they launch with gusto and full concentration into ''Blues in the Night.'' The result is a rich and rhythmic big-band sound that quickly fills the house and makes anyone not playing want to start dancing.
In an age when most families bemoan the lack of time for togetherness, the Wolff family manages to have it in abundance - both because there are so many of them and because there is no television in the house. The hours for making music together have been carefully set aside. During summer months, when homework is no longer the top priority, they often practice together between two and three hours a night.
''It's fun and relaxing, and it has made me feel a lot closer to my younger brothers and sisters,'' says 21-year-old Ginny Wolff, a college junior. Like most in the family, she plays not just one but two or three instruments.
No one in the family can remember exactly who or what propelled them into a family band. Mrs. Wolff, who had hoped as a young woman to become a concert pianist and now is an organist in her church, taught each child to play the piano as a part of growing up. By watching the ads for second-hand instruments, the Wolffs gradually began to acquire everything from trombones and zithers to violins and saxophones. A school band teacher began giving some of the older children free lessons.
All Wolffs agree that some of the impetus for performing as a family started with a welcome-home celebration several years ago for Stephen, the oldest son who was away at college. Now a graduate student who loves music and plans to teach it at the college level, he was told on his arrival home to go in a back room and wait a few minutes. His sisters and brothers scrambled to get their instruments together in the kitchen. Then, as he came down the hall, they launched into what Ginny Wolff recalls was a rather poor but decidedly enthusiastic rendition of ''I Love You Truly.''
''We really couldn't play it very well, but he was so surprised and excited about it all that he jumped right up to the ceiling,'' she says.
When Stephen then took a job that summer in a music and instrument business in nearby Mundelein with a man who also happened to be the high school band director there, it was only a matter of time before everyone in the family began taking lessons and started to practice together as a group.
Even Richard, the children's father, who manages four printing plants in the Midwest for the United States Navy, began to get involved as he drove the children back and forth from lessons and group practice in the band director's studio. When he was asked what he could play, he said he could manage ''a little'' on the accordian. The band director, who had already jokingly begun to refer to the Wolff family as a band in itself, said, ''Your band doesn't need an accordian - it needs a drummer.'' Mr. Wolff now practices daily - legs and arms a picture of constant motion - on a set of bass and snare drums and surrounding cymbals.
Only the older children had the luxury of choosing which instruments they would play. The youngest automatically net tambourines and maracas. Those in the middle are expected to fill in according to the band's needs. Still, nine-year-old Julia had to switch from the saxophone to a flute when her hands turned out to be too small to reach all the finger keys.
Though they started playing just for pleasure and still sometimes play free for charity fund-raisers, the Wolff family band now usually charges a fee for performances at weddings, dances, civic groups, county fairs and the like. The dollars are put toward the children's tuition - five are currently in college. That fact is assuredly part of the pull that brings the Wolff family together from far and near for most bookings.
''I wouldn't say the amount we get is overwhelming, but every little bit helps,'' Mr. Wolff says.
The family plays everything from polkas and jazz (their favorite) to Dixieland and soft rock. But you won't find any hard rock on their schedule. They don't like it. And they won't play country-and-western music because they don't have any guitars (other than Mark's electric bass) and because it wouldn't allow everyone in the family to participate. Usually younger and older children are teamed up to play the same kind of instrument for more convenient coaching and backup during performances.
Everyone, it appears, has a job. Mr. Wolff handles the scheduling and serves as the announcer, often starting with a joke that gets his children as well as the audience laughing. Mrs. Wolff, who arranges much of the music herself and is currently taking classical jazz lessons, sees to it that the music is in order and in place. Mark, a senior in college, generally rehearses the group in practice sessions and tries to tone down anyone playing too loudly.
Though they look on themselves as a dance band - and most of the children say nothing makes them happier than to see listeners take to the dance floor - Richard Wolff concedes that sometimes the audience is so fascinated by the phenomenon of a large family that they never quite get around to dancing.
''Sometimes they just sit and watch - I guess they've never seen anything quite like us before,'' he says.
For many of the children, the commitment to music goes well beyond family boundaries. Eight have won awards in schools where they've played in bands and orchestras over the years. And 10 now play in the Chain O' Lakes Orchestra in nearby Fox Lake, Ill. The Mundelein Municipal Band also leans heavily on the Wolffs for its corps of performers.