Hi Tammy - 

I have worked in units that work with adolescents under 18 in native american communities and have been able to successfully justify a W9 waiver based on the fact that not doing so significantly impairs study recruitment and participation. I don't think my institution has the added complication of not issuing gift cards for <18 y.o., though - is that a policy or some sort of limitation of the system?

This is not a super helpful response as I don't know how our finance office (which is the central office that approves our gift card programs) documents and determines that a W9 waiver is warranted/approved. If no one has a better answer/guidance I can reach out and ask what our university relies on policy or documentation-wise to allow these sorts of situations if that is helpful.