Box 5 amounts in excess of box 1 is considered taxable income to him to report on his return if he is required to file one. The taxable portion would be reported like wages which makes it earned income...
Please see the filing requirements for dependents:
- Your earned income (money you made by working) exceeds $12,400
- Your unearned income (interest, dividends, capital gains, etc.) exceeds $1,100
- Your business or self-employment net income (gross minus expenses) is at least $400
- Your gross income (earned plus unearned) exceeds the larger of $1,100 or your earned income (up to $12,050) plus $350
