If you want your child to learn: how to face stronger opponents, how to handle the disappointment after losing, how to be humble after winning, how to think, how to be patient, or how to persist, a few lessons are definitely not enough. It requires years of learning. Learning chess is a step by step, gradual, long term process. It's not a cram for tests. If you push them to learn too much in one session, they will only get a few points and forget everything else. They won't be able to use the knowledge they learn. Practice is much more important in chess than knowledge.
Like math and music, chess requires persistent learning and practicing, almost daily.