@Jellykat
Worries me slightly that testing is 6-17 yr olds, how can a 6 year old make an informed choice?
Are participants paid? If so i can imagine some parents volunteering their children to get money..
Please read up on trial design.
This will have been a highly scrutinised, meticulously planned trial with a protocol which would have gone through an ethics board. Of course they won't give out cash or financial incentives that could lead to coercion of children to participate.
Incentives will be age appropriate- maybe vouchers for a popular store, stickers, sometimes kids get scan pictures if appropriate and relevant (i.e, we've given out colourful pictures of brain scans in a neuroimaging trial). Please have some level of trust in the clinicians and scientists who are running this- many of whom are pediatricians who have child public health as their personal interest.