Cheshire Figment is correct. Assuming taxes were not withheld, then child is subject to self employment taxes (Social Security and Medicare taxes) - so he would be required to file and pay the self employment tax.
If there taxes withheld from the pay then there would likely not be a requirement to file (as the income would be too low to require a filing). If taxes were withheld (above and beyond Social Security and Medicare) then the child will likely get a refund of those taxes assuming the child does not have much in the way of other income - so while its not required to file under this fact pattern, the child should file.
Also of note in this case, the child's income can not be added to the parents return. That accommodation is permitted when the only income a child has is on investment income (like interest and dividends). Employment income is not afforded this accommodation.
If you (or her) can afford it, fund an IRA in DDs name. Its great to start an IRA at such a young age.
I hope this helps (I am a tax practitioner by trade).