The phrase "childish notions" refers to ideas or beliefs that are silly, naïve, or not mature. It means having thoughts or opinions that might seem childish or not very grown-up. Full definition
The youthful nature of Nara's figures conjures childish notions of the star, varying from from earning a gold star as a reward for good work in school to the optimism of childish bromides such as «shoot for the stars» and «wish upon a star.» (supertouchart.com)
Because the world, at this point, insists on giving respect to such childish notions as imaginary gods, it is one of the few ways crazy people can garner any respect for themselves. (religion.blogs.cnn.com)