One thing you may want to consider (and perhaps you know the answe already?) ..... how important is replication, vs. something similar that can serve the purpose? You may want to discuss with the "powers-that-be", before going ahead with the project. For someone who does not sew, they maybe asking for the same, but never thinking about how it could be better with some changes.
Being in a pre-school setting, I would expect this cushion will see a lot of wear. You may want to consider something more rugged than a quilting cotton for your fabric choices. Perhaps an upholstery assortment?
Another thought, if going with traditional quilting cottons, what about using a selection of novelty prints. Would be fun for the kids to explore the fabrics, and of course, the I Spy game could be played.