I think that's provably untrue based on the fact Saturday morning cartoons were massively popular as a curated content feed on TVs through the 70s, 80s, and 90s. Kids (including me at the time) loved them and sank many hours into watching them. They were wholly approved by my parents, to the point where sometimes my parents would watch with me. Unless kids have fundamentally changed (which seems unlikely) the differentiating factor is almost certainly that kids simply now have access to far more unsuitable content.