WASHINGTON—During a congressional hearing Wednesday aimed at holding tech companies accountable for children’s safety online, Meta CEO Mark Zuckerberg gave testimony in which he assured concerned parents that he was keeping a very close, personal eye on teen accounts. “I personally spend most days and nights in front of my computer, closely monitoring every piece of content uploaded by your young teenagers, so there’s no need to worry” said the 39-year-old billionaire, explaining to parents that there was no way for strangers to exploit underage children without him seeing the private messages in real time. “There’s not a single image your precious son or daughter has sent through Instagram, Facebook, or WhatsApp that I haven’t seen and preserved on my own hard drive for safe keeping. I’m out there every day looking at their photos and making sure the racier stuff doesn’t get into the wrong hands. When I see …