I believe they open about 6:00pm. As far as young kids, it would depend on the child. I've only eaten there twice and both times I saw only a couple of kids in there, but they were always well behaved. Make an early ADR and if your little ones start to act up, just take them out. No problem. The only problems I've ever seen with little ones at signature restaurants are when the parents refuse to take them out. This happened at Citricos last May. There was a little girl that just kept throwing a fit and the parents just ignored her. Those people were getting some dirty looks. Well behaved kids are always welcome at restaurants at WDW. The only ones they are not, that I know of, are Victoria and Alberts and Bistro de Paris.