The phrase "childish nonsense" refers to something that is silly, immature, or not worth taking seriously. It implies that the topic or behavior being described lacks maturity or rationality. Full definition
Its just junk childish nonsense to make excuses for what I don't understand. (justarsenal.com)
This is one of the worst pieces CNN has ever seen fit to publish - what childish nonsense! (religion.blogs.cnn.com)
that is like a 5 year old mentality... how can you take these people seriously... You want to put people who think such childish nonsense in charge of the human race?? (religion.blogs.cnn.com)