Cut the shapes out of the paper printout of geometric shapes and place the cut-out paper shapes aside.
Pick up one of the cut-out paper shapes and place it on top of one of the household sponges. Place a straight pin through the paper shape and the household sponge to hold them together. Repeat for each of the remaining paper shapes and household sponges.
Pick up the scissors and one of the pinned household sponges. Use the pinned on paper shape as a template and cut through the household sponge following the outline of the paper shape. This will create a sponge in the exact same shape as the paper template.
Open one of the containers of poster paint and pour a puddle of paint onto a paper plate. Repeat for each of the remaining containers of poster paint.
Set the paper plates side-by-side on a table, and place the sponge shapes in the center of the table. Place a piece of heavy-weight paper on the table for each child.
Instruct the children to pick up one sponge shape at a time, press it flat in one of the paint plates and then stamp it onto the paper.
Use the baby wipes to cleanup.