Generally speaking, in Japan it's pretty rare to see families out to dinner at any place other than fast food joints, cafes, or chain restaurants like Denny's or Jonathan's.
In some traditional households, moms are still expected to stay home with the children, while dads eat out with colleagues and clients. With others, parents are worried that young kids will disturb diners with their fussing and crying. And then, of course, there are the families concerned about smoke. Despite the addition of no smoking sections at many eateries in recent years, most are ineffective because it's not practical to install barriers that keep the smoke from spreading everywhere (and even when it is practical, many establishments just don't bother).
But change may be on the horizon. Perhaps it's a sign of evolving consumers, or restaurants, worried over ever-diminishing revenues in tough economic times, have begun to innovate.
Regardless, a few Japanese pub chains have started installing windowed "kids rooms" that parents can monitor from the main dining area or private rooms
Outfitted with toys, TVs and video games, the rooms appear to provide the essentials to keep many kids occupied, but I haven't had the chance to see any in person, so I can't go so far as to vouch for their quality.
The above photo comes from a yakitori chain called Toritetsu, which is part of the Asrapport dining group.
