I am not a tax expert. My child is in a similar situation. My understanding is that because the child in this question is a dependent, on his tax return his standard deduction is the greater of $1100 or his 'earned income' plus $350, both capped at the non-dependent single standard deduction of $12,500. Since the child has no earned income, he would be required to file a return, and pay income tax on all but $1100 of the stipend.
