New Delhi, June 15 -- PARIS - The children who opened TikTok or Instagram on Monday morning in France and Britain may, if their governments get their way, be among the last to do so without a fight. On the same day, President Emmanuel Macron and Prime Minister Keir Starmer each announced plans to bar children from social media - Macron drawing his line at 15, Starmer at 16 - in the most sweeping coordinated European challenge to Silicon Valley's hold on adolescent attention since the European Union's Digital Services Act took effect.

What made Monday striking was not the policies themselves, which both leaders had been telegraphing for months, but the timing. The announcements landed within hours of each other, projecting the image of a ...