In desperation, humans will cling to any hope.  The idea Thorsten S. mentioned about using orphans was spot on.  There is no need to pull the children from their families when such an abundant source exists.  Many of these older orphans would relish a chance to seek revenge for the deaths of their families. Although, once the new soldiers start winning, I suspect families would seek to participate.

I would suggest that either the genetic changes are made somatic cells instead of to the germ-line (or sterilize the children.)  Otherwise, the human race will be extinct.

To sell it, promote the successes and market the program as the only hope of humanity.  Celebrate the children as heroes.  Interview them.  Mourn when they fall.