I have a vague memory of either our electrician or home inspector telling us that the outlets in our recently renovated condo do not need those plastic child safety covers in order to be child-proofed because the circuit breakers are in some way better now than when I was a kid. Is there any truth to this?
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.