Earned Mission Trip Credit

We have a member who donated a lump sum of money to help kids with the cost of their mission trip.

The donor wants the kids to earn credit towards their trip by working around the church (helping in the nursery, running worship slides etc.)

Can we credit individual balances due for the mission trip when kids work around the church (credit amount set at $16 per hour)?

This credit is done by transferring the funds and not cutting a check to the missionary. I'm afraid the IRS might see this as taxable income to the missionaries.