We do a lot of walking around the neighborhood with kids, which usually involves some people getting to intersections a while before others. I'm not worried about even the youngest going into the street on their own—Nora's been street trained for about a year—but we have to be careful about what signals we send to cars. Someone standing at an intersection facing traffic looks to a driver like they're waiting for the opportunity to cross.
Waving drivers to continue doesn't work well: they tend to slow down significantly, and many of them will wave back in a misguided attempt at "no, you first" politeness. Instead, what seems to work well is turning your back to the street:
This isn't perfect: some drivers still read anyone stationary near an intersection as intending to cross, but it's pretty good. And it's especially good for little kids: not only do they often like to look intently at passing traffic in a way that is concerning to drivers and passers by, but it's a clear signal to the parent that the kid knows it's not time to cross yet.