Are child safety covers still required on modern outlets?
Along with arc-fault breakers protecting some areas of the home, "tamper-resistant" outlets are also required. They don't allow insertion into just one slot--both slots must be pressed together as an actual plug would do. 

I get the sense that you're asking about protecting little people. I'd either use plugs or install tamper-resistant outlets if I had toddlers, regardless of arc-fault protection.