The ROTH IRA (USA) requires earned income to be allowed to deposit (add) money. There is no rule that the money earned is the money deposed. If your kid has a job, and you have extra money, look into opening a ROTH with them. Kid spends their money (or not), and deposits your money in their account. Bingo setting kid up for old age.
Regardless of income but subject to contribution limits, contributions can be made to a Traditional IRA and then converted to a Roth IRA.[23] This allows for "backdoor" contributions where individuals are able to make Roth IRA contributions even if their income is above the limits.