I am very pleased to see this change. Irrespective of GDPR, it must be the right and ethical policy. I am in the UK where the approach on privacy for children may long have been a bit tighter than in the USA. But there are clear guidelines of the US National Genealogical Society. The relevant extract is a commitment to
“inform people who provide information about their families how it may be used, observing any conditions they impose and respecting any reservations they may express regarding the use of particular items;
require evidence of consent before assuming that living people are agreeable to further sharing or publication of information about themselves;
convey personal identifying information about living people—such as age, home address, genetic information, occupation, or activities—only in ways that those concerned have expressly agreed to;
recognize that legal rights of privacy may limit the extent to which information from publicly available sources may be further used, disseminated, or published”
Under the NGS guidelines, children should give consent for information about them to go on Wikitree. There must be a question over whether children under 13 can be regarded as able to give informed consent even if they are told that a relative intends to put some information about them on Wikitree. For me this is a question of ethics.