It depends on whether or not your kids were earning an income.  If so, then they will need to file a 2015 income tax return.  This applies to dependents who earned wages totaling over $6,300, as well as self-employed dependents who took in more than $400 over the course of the year.  They would also have to file if there's investment income over $1,050, or any combination of wages plus investment income.