We love Napa Rose and have been taking our kids there since they were tiny. They have a fabulous kids' menu, including the Balboa Beach Sand dessert. When our kids were little, we'd order one course and we'd put in our order immediately - we were in and out in about an hour. As they grew older (now they range in age from 8 -16) we'd stay for longer dinners and order coffee at the end.
As a previous poster mentioned, it really does depend on the kids, and I'd say it also depends on your expectations. Our kids have always identified our meals together as one of their favorite parts of Disney, so eating at signatures isn't a drag for them. Even our very energetic youngest son behaves well in restaurants, and interestingly, the nicer the restaurant the better his behavior. We time the meal for success, and we don't mind when the menu items are pricey but the dinner goes quickly. Also, one of us was always ready to take one of the kids out immediately and take a meal to go - even at the first sign of a louder-than-appropriate voice volume. We've never had to do that, but we make all reservations prepared to take action if necessary, and with sensitivity to the dining experience of fellow guests.
I was initially reluctant to take our kids to signatures based on some of the comments on these boards, but I'm glad that we did. Our kids have had such positive experiences in a welcoming environment at Disney signatures (both WDW and DL) and on
DCL. The positive comments from diners around us have always helped to reinforce positive behavior, and really prepared our kids at an early age for fun and interesting dining experiences in our non-Disney travels.