A minor earned $2k of income on a W-2.  No taxes were withheld, so the minor does not need to file a tax return since they are under the income threshold for both federal and state.

The parents plan to setup and fund a Roth IRA for the minor using the minor's own funds.  

Question:  Is a tax return required to be filed to "prove" the earned income for the Roth IRA contribution?  Or is the W-2 proof enough?   I would think the W-2 is enough proof and no return is required but can't seem to find any literature to prove this.  Obviously no one will ask for the proof unless there is an audit or an issue down the road... 

Thanks for your input!