I have a 14 year old dependent who received a 100-NEC for more than $600. How do I enter this on my taxes? Do I have to submit his own tax return?

MY DEPENDENT HAD A JOB

If your dependent has a W-2 for his after-school job, summer job, etc. you do not include the information on your own return. You can still claim your child as a dependent on your own return.  He/she can file his own return for a refund of some of his withheld wages from boxes 2 or 17 (he won’t get back anything for Social Security or Medicare), but MUST indicate on it that he can be claimed as a dependent on someone else’s return.  (Supervise this closely or prepare it for him!)

If your dependent’s earnings were over $400 and were reported on a 1099Misc or 1099NEC then he must file a return and pay self-employment tax for Social Security and Medicare.

You might also want to use free software from the IRS Free File versions:

https://apps.irs.gov/app/freeFile/

Not on your taxes. The 1099-NEC usually means your child worked similar to a job but had no Medicare or Social Security tax withheld and now it must be paid. An self employment work over $400 requires filing and paying the additional tax.