A few weeks before the concert, have the kids get together a pick a song to sing. For preschool children, keep it simple. Go for a song such as "Old McDonald," or for a holiday song, go with "Jingle Bells" or "O Christmas Tree." These are simple songs that younger kids can remember and parents can sing along with. If you want to create an original song lyric specifically for an occasion such as the end of the school year, choose a song with a simple melody such as "Twinkle, Twinkle, Little Star," and change the lyrics to something like, "Summer, summer, here you are."
Throughout the year, you have introduced musical instruments to the kids, such as plastic flutes and tambourines and drums. Divide the children up into sections, and teach them a simple song to play on the instruments. Have the sections play three or four short songs together, with each section having a solo.You can also have each section play a separate song.
A few months before the concert, have the children learn a simple dance routine. You can do this with all the children together, or separate the children for a few different routines. For instance, the girls can perform a ballet while the boys perform a tap dance. Provide the children with mini-ball gowns and tuxedos, and have the boys and girls perform a joint waltz together. Dress the children in cowboy/cowgirl attire, and have the kids perform a square dance for the teachers and parents.
Create a short musical from familiar nursery rhymes for the kids to perform. For instance, create a musical around the nursery rhyme "Jack & Jill." The musical can include short speaking parts but should mainly consist of the students performing the nursery rhyme to song. This idea works for any short nursery rhyme, such as "Twinkle, Twinkle, Little Star" or "Simple Simon."