How can I report a Roth donation for my children on my 1040? They are minors and do not need to file a return

You do not have to report Roth Contributions set up for your children.  You should consult with legal counsel, however, because your nomenclature of "Donation" could be problematic.  

you posted that they don't have to file a return. so the question becomes do they have earned income (w-2 or self-employment income) at least equal to the contribution?

A ROTH can only be purchased with earned income.  Do your children have jobs to earn the money for the ROTH IRA?  Are they working for you in a business?  If they earned money and paid income tax they need to file their own return.