I am not sure if this will work or not. When my daughter was a gold medallion and flew as a lap child domestically I was unable to enter her skymiles number in her reservation. We never received a boarding pass for her either- it was kind of like she didn't exist. It might work internationally as lap children need to have tickets, but again, I don't know if they will have a skymiles number associated with that ticket as they don't earn miles. How about if your friend makes one of the parents silver instead?