It is not 100% decided yet on how children’s data is to be processed and handled. The authorities don’t seem to have found a solution to this particular problem yet. In the meantime, we strongly advise you only ever store the least necessary amount of personal data on children that you need. That is, even with the parents’ consent (and remember, knowledge doesn’t equal consent). The best thing to do would probably to avoid storing any data on minors at all!