kid stuff vs youthful

kid stuff

noun
  • Something that is easy to do or easy to understand. 

  • Something done by, used by, or characteristic of immature people, especially children. 

youthful

adj
  • Young or seeming young. 

  • Characteristic of young people. 

How often have the words kid stuff and youthful occurred in a corpus of books? (source: Google Ngram Viewer )