Since your son is a dependent and has more than $1,100 of "unearned" income, i.e. investment income, he is required to file a tax return and report the 1099-DIV. (This is assuming he is not blind.)
Being a dependent does not give him an exception to filing a tax return. In fact, it's just the opposite. If he were not a dependent he would not have to file a tax return for so little income.
Being a minor makes no difference at all. The filing requirements are the same for anyone under 65 years old.
If the 1099-DIV is your son's only income, there is an option to report his income on your tax return, but it's generally not a good idea to do that. The only advantage is that it's a little less paperwork, but you could end up paying more tax than if he files his own tax return.
