Piccolo voices, primo productions. Children sing under wing of Milan's famous LaScala. OPERA WITH KIDS

THE colorfully uniformed soldier marched erectly - perhaps a bit stiffly - across the stage to the sound of a jazzy little march tune. The devil, dressed in red with forked tail and pointed ears, welcomed him with open arms. The music from the orchestra pit swelled to a huge climax. The great velvet curtains swiftly closed on this final scene. Immediately the audience burst into shouts and applause - even loud whistles and raucous screams.

The scene was from Igor Stravinsky's ``A Soldier's Tale.'' But this was not an average Teatro alla Scala audience in Milan, nor was it a traditional La Scala cast on stage.

The oldest member of the enthusiastic audience was only 12, the youngest but 8. And the characters on stage were not well-known international opera stars, but fanciful marionettes, created by Luigi Veronese especially for this production.

The wonderful music, youthful exuberance, and excitement were part of Teatro alla Scala's ``musical season for children and young people,'' aptly titled La Scala for Children.

The program was headed by two musically knowledgable, resourceful, and inventive young men, Sylvano Lupetti and Gregorio Sangiovanni.

La Scala for Children opened last October with 18 performances of ``The Dreams of Mr. Blek,'' ``a fable of the musical theater for puppets.''

Based on B'ela Bart'ok's music for two pianos, the original story written for the production was by Tinin Mantegazza - who, along with wife, Velia, created the bright, toylike setting and the fanciful animal puppets who ``peopled'' it.

While the idea of presenting musical theater experiences for the young is neither new nor novel, La Scala's approach is.

``You see, the tradition in the past,'' says Mr. Lupetti, ``has been to take musico-dramatic works written for an adult public and - if these operas have stories even remotely connected with the world of children (like Humperdinck's `H"ansel und Gretel' and Rossini's `Cinderella') - schedule a single performance for children of all ages in the opera house during the work's regular run.

``The challenge of this kind of presentation is manifold. The works are much too long for the attention span of most children. Then, the story Rossini used in his `Cinderella,' for example, is not the same version the children know so well. And an opera house filled with two or three thousand children! Have you ever heard the noise level when two or three thousand children try to sit still and be quiet? It may not bother the average parent, but for the artists on stage, it is certainly disconcerting!''

``What we at La Scala try to do,'' Mr. Sangiovanni goes on to clarify, ``is to select short works that in performance are well within the attention span of children - pieces of unquestionable musical value by master composers, but which have an immediate appeal for young audiences.

``We're also aware that what appeals to a four-year-old is not the same work that will appeal to a 14-year-old. And most important, we schedule our productions, not at La Scala, with its 2,000-plus seats, but in small, intimate theaters and concert halls.''

One of the highlights last season - which included a ballet program in May for six- to 12-year-olds, featuring Saint-Sa"ens' humorous ``Carnival of the Animals'' and Benjamin Britten's self-educating ``The Young Person's Guide to the Orchestra'' - was a joint production with Milan's Piccolo Teatro of Kurt Weill's ``Der Jasager'' (``The Yes Man'').

Weill is best known for his songs ``Mack the Knife'' and ``September Song.''

In Milan, ``Der Jasager'' was presented for children between 11 and 14 years of age - 21 performances altogether in Teatro Piccolo's intimate 400-seat theater.

The Children's Chorus of La Scala Opera, along with tenors and basses from the Milan Conservatory of Music Choir, made up the on-stage chorus.

The chamber orchestra in the pit consisted of instrumentalists from Milan's venerable old City School of Music.

With the exception of the two adult parts sung by members of the La Scala Opera Studio, the soloists were children between the ages of 7 and 13 years, about 20 youngsters altogether.

When productions of such inherent musical value are presented in carefully prepared productions, as regularly occurs with the La Scala for Children program, the future of the lyric theater looks promising indeed.

Appropriately, La Scala for Children has set a high standard for the new season that opens here in Milan in a few weeks:

``Nothing less than the best.''