I think they're thinking about the same sorts of things that we're picturing. You're right in that there are ethical issues that can't be trivialized, and I'll try to reassure you that the community is thoughtful about them.
Right now we're primarily talking about seeing children who are presenting with something that's wrong with them and we don't know what it is. In many cases, we don't know what the future is going to hold for them. The idea is that if you can identify the answer more quickly, you can get them on the right path. That may not be a cure, and it may not be a treatment, in the sense of a fancy device. It may be that the child needs an ultrasound or something other children don't need, or perhaps new interventions in the school.
If you do those tests for diagnosis, you may also stumble across other things that weren't the main reason for doing the test but are also relevant for their health. We feel we are obliged to deal with those if they affect their health in childhood.
If we scale it out to the bigger population, you could see at some point asking for this for all children who are healthy before they get sick. We're not there yet, but we need to think about it so we don't do it badly or rush into that.