童心

1. Origins, structure, and basic meaning

• Structure: 童心(どうしん) is a noun for childlike innocence or a playful childlike spirit.
• Basic usage: Returning to that state appears in 童心に返る, while retaining it appears in 童心を失わない.

2. Common pitfalls and similar expressions

• Age and state of mind
  • It is not limited to children; it can describe an adult recovering or retaining childlike innocence and delight.
• Change and retention
  • Use 童心に for returning to that state and 童心を for not losing it.