Here are some ideas for collage art with young children.
Seed Collage
Children glue different kinds of seeds on paper.
Sand Collage
Children first draw an outline of their picture with a black ink pen, then fill it in with sand. They use a glue brush (inexpensive dollar store brush) to paint glue in the area they want a particular color of sand, then sprinkle that color of sand over the glue using their fingertips to pinch the sand. They shake off the excess sand onto a paper plate. Then they can paint on more glue for the next color.
Paper Mosaic
Colored paper was pre-cut into one-inch strips. Children cut the strips into pieces to glue onto a piece of black construction paper to make a mosaic.
Paint Card Mosaic
Paint sample cards were pre-cut into different sizes of squares, rectangles, and triangles for the mosaic pieces. The paint sample cards are free from hardware stores. Children glued the mosaic pieces onto a square of white construction paper to make the mosaic (I recommend a small square, about 6×6 inches). Each child chose a cup of mosaic pieces that were all one color, but of different hues.
Monster Masks
Children used several collage materials of their choice from our art center to create a monster mask on a paper plate.