Diners are usually great places to take kids, since they offer exactly the kind of food kids like for decent prices. Most offer kid-friendly menus, too, not to mention coloring pages. Speaking of kids, in some states, diners can't serve alcohol if they're located too near a school.
Don't expect haute cuisine from a diner. Diners are best at providing good, wholesome food at a decent price. While they may vary in quality, you can generally get an acceptable meal for ten dollars or less, including coffee and a slice of pie.