US employers do not pay for travel to the job and I would not pad it, but your other ideas have merit. Part of the idea of employing young people is so they can realize some realistic work experience. So, if it takes 15 minutes a day for about 8 trips (7 days plus 1 for orientation) at minimum wage rates of $15/hr, then $30 total for the whole job would be fine. Make the payment in $5 bills x 6 with the envelope addressed to both of them and leave it to their partnership as to how to divide it. Pay after the job is done. Offer a reference letter if they did an excellent job.