Assuming this child is unmarried, under 65, and can be claimed as a dependent on someone else's income tax return (for example, his parents' income tax return), a federal return is required if ANY of the following is true:
1) Unearned income is more than $900.
2) Earned income is more than $5450.
3) Your gross income was more than the larger of -
a. $900, or
b. Your earned income (up to $5,150) plus $300.
4) You have at least $400 in net self-employment income.
5) You owe uncollected Social Security tax on tip or imputed life insurance income.
6) You received any advance EIC payments
7) You had wages of $108.28 or more from a church exempt from Social Security.
8) You owe excise taxes on a retirement plan account or distribution.
9) A few other rare and arcane cases that are extremely unlikely to apply here.
However, even if not required to file, you should file to obtain a refund of taxes withheld from your salary or if you are entitled to any refundable tax credits.
You should also file if you received any Forms 1099-B or 1099-S (usually from the sale of stocks, bonds, real estate, or other property), even if the sale was at a loss or no profit in order to report your basis.
If your state has an income tax, they may have different rules as to who must file a state return. Every state has different rules. Check the instruction booklet that comes with your state tax forms.