When our kids got lost

it happened again last weekend: when we left the restaurant, we suddenly had only one child. Luckily, we were in a fairly safe place - the restaurant floor of one of the big department stores in Tokyo. But still, you never know with children. They can always bump their heads or fall down an escalator, or get into the elevator and get off on god knows which floor.
​Kids love to play games and ours wanted to play hide and seek with their parents. They play it in daycare, even if they are not that good at hiding yet. But it is fine to play in the park at home, where you know what is dangerous and the childcare person can find you. It is a different matter to play and run around in a place where you might get lost, not to speak of the fact that you are underfoot and in the way.
But they also have to realize that they need to talk to us before they run off, if they want to play hide and seek. Otherwise, it is all hide and no seek.
If you are a parent yourself, you will know that we were first really worried (although we could actually hear them most of the time). And then we got annoyed (since we knew they were on the same floor as us). And when we found them, we got really mad and relieved at the same time.
They did not get the icecream we had promised, and neither did their sister. Which was a bit unfair, since she had not run away and stayed with us all the time. But she did not get yelled at, which our other two were. Until they cried.
Much as it hurts your heart, if you want your children to learn a lesson that changes their behavior, it has to hurt emotionally. If you scream at them when they do something wrong and then get so sorry you give them icecream, what kind of signal are you sending? You need to be consistent as a parent, and consistency means rewarding good behavior and discouraging bad. Although physical punishment is out, you need to figure out ways that makes them remember what is desirable and what is undesirable. No icecream for running away is an effective way of making the negative behavior undesirable, although the emotional pain of disappointing your parents and making them angry enough to scream at you is a much more effective deterrent for the future.
Not that it will never happen again. They will run away, if not before when they turn teenagers, although at that point we hope that they will be gracious enough to come back on their own. But they will think twice about it.
Not that I am proud about it, mind you. But when you sometimes have to manage multiple kids on your own, you have to have a way of controlling them from a distance. Short of putting them on a leash, the only way you have to control them is using your voice (since they do not pick up their mobiles like a grownup would. At least to read the caller ID). We have actually considered putting them on leashes when we are in airports, but now voice works well enough.
So why did this happen? Well, the first reason is simple: we did not make sure they understood how dangerous and problematic it can be when they get lost. The second reason is that we did not control them well enough, but we were so relaxed after the nice lunch (during which they were unusually well-behaved) that we let our guard down for a moment.
But I am confident it would never have happened if we had talked to them in advance. We usually do that, and it works much better than what people believe that kind of thing can work with small children. They may not have a very good grasp of time or know math, but they understand that cars are dangerous and if appropriately briefed they can behave surprisingly sensibly.
But we missed that. That will be our homework: how do we remember it next time? What do we say? How do you do it?