Kids menu at both.
San Angel gets mixed reviews. It certainly isn't tex-mex, but has dishes that I think are more central Mexico - we like it and think the food is good, but a lot of people are disppointed. Reviews of service have been not always great, though our service has been unremarkable either direction. The restaurant is sort of dark and the tables are very close together - some people like this, some don't.
Flying Fish is one of my favorite restaurants. Its a little fancy for kids unless you are fairly confident in yours (we went with a six and seven year old who did fine, but I wouldn't have gone when they were three and four). Its fairly expensive, but the food is generally excellent (lots of fish on the menu, though).