Vegetables, smoky-sweet from the grill and zingy with lime juice, transform simple cheesy tortillas -- comfortingly familiar to children -- into something sublime. Other fresh, seasonal, vegetables, such as eggplant or fennel, would make a lovely addition to the line-up here. And do try to hunt down the chipotle peppers, which add their own delicious hit of smokiness: they're available canned, in the Mexican foods aisle, and you can puree the entire can and store it in a jar in the refrigerator for instant flavor-boosting. (But if your kids are spice-shy, stick with the paprika.) - By Catherine Newman