Really, the only restaurant in WDW that is not ok for kids is Victoria and Albert's as they have an age restriction. Everywhere else can be family friendly, including the signatures. Of course some places are more fun for small kids than others. Any of the character meals. We have done most of them and never really had a bad experience anywhere. We are not crazy about the food at Hollywood and Vine (HS), but it is not bad if your kids like the Playhouse Disney people. Rainforest and Dino Cafe are fun as long as you kids are not too little or frighten easily. They are pretty loud and the stuff a bit realistic. Even by 5 my little guy was a bit hesitate but always did ok there. The sci-fi (HS) is fun for 6 and up. Funny old flicks might be a bit much for really little ones. Eating in any of the castles is a huge treat. You can do CS at Be my Guest if money or getting an ADR is an issue.
We like to do a mix. Our youngest is now 6. A few character meals, a few fun places like Prime Time or Dino Cafe and a few nicer signature places. For these places, maybe be sure you child has had enough dining experience that you can predict positive behavior and book the earliest time for dinner. I love a few CM but also like enjoying and exposing kids to a little more formal dinning and WDW is the perfect place to do that. Kid meals available everywhere.