Unfortunately "it depends". See the below article for some common rules of thumb and guidance.
https://turbotax.intuit.com/tax-tips/family/at-what-income-does-a-minor-have-to-file-an-income-tax-r...
If your child has earned income of less than $14,600, they are not necessarily required to file, but might want to try to recoup some of the federal taxes that may have been withheld.
If your child has unearned income (interest or dividends) of less than $1300, again, they do not have to file.
If your child has tips or self-employment income of more than $400, they need to file a return.
