OK, this is flat out amazing. Cowacca is a small strap and ring for kids to hang onto. It just clips on your belt, or backpack, or stroller, or wherever you need it to not lose a kid.
It is made of maple and leather. It was designed by Ono Rinao for a 2005-6 exhibition, Codo Mono Coto, which is a tricky Japanese way of writing "Kids Stuff." It was a design show about living the kid-included lifestyle.
Cowacca is still available at AssistOn, or you can rig your own, because now that you see it, it is the most obvious thing in the world.
Cowacca, Small strap for kids, ¥3,675 [assiston.co.jp via likecool, thanks dt reader rolf]
Codo Mono Coto shop/portfolio page [codonomocoto.jp]
Or, you know, just hold their hand?
I guess the design is clean and simple. But I'm with Nelson, sometimes the best design is no design at all.
I think the substitute good here is a belt loop, not a hand.
When kids are still very small, but ambulatory, it's hard to hold their hands, because their hand reaching up and a tall person's reaching down often do not meet.