depends on their age. There are loads of chains that cater for kids. The ones I relied on for years when they were young were: Pizza express (they have toy packs with little card games and colouring books for every child, and the chefs often give them free paper hats and let them watch the pizzas going in.) Giraffe - they get cute dayglo giraffes to stir their drinks with and the menu has adult food not just LCD burgers. Loads of people recommend Wagamama - never been in because it's inevitably next door to a restaurant my DC want to try even more. But it's a similar format - child friendly with high chairs and kids menus as well as grown up food. Also - Nandos isn't bad at all. Only sell chicken, but there's a good variety and the food is fresh. I had home made humous last time, it was really good. You might have to asteer the Dc away from the never ending soda stream and frozen yoghurt pots, but apart from that, it's quite cosy. In London there's Smollenskys, especially designed for children with table magicians who make balloon figures and do tricks, and a huge screen with cushions, so they can watch tv after they've eaten while you enjoy a coffee. For older children, Byron burgers are great.
Most Italian restaurants are child friendly. There is also Frankie and Benny's but they are a bit hit and miss in terms of the quality of the food.
We play a LOT of eye spy while waiting in restaurants - play with colours instead of letters for little ones and go prepared with stuff - a new comic or something is good and if all else fails hand them your phone
Also, don't know if you have Jimmy Chungs or similar chinese buffet places? Tend to be child friendly as there is no waiting and under 3s eat free and they can try lots of different things - there is usually plainish noodles and chips etc for fussy eaters - also they can always have the chicken balls without the sauce and have ketchup instead.
The trick with young ones is to go somewhere the food comes quickly (Wagamamas can never be beaten on this one) and to limit yourselves to a main meal only and possibly coffee only if they are having deserts. Don't even think of ever having a starter - ever!
As for the bill with the DC are still eating their desert so that you can leave when you want and aren't hanging around waiting for ages.
Will never step foot in a Frankies and Bennies again, they are truely dire. Over favourite is a local Italian, great kids menu and friendly. Not a huge fan of the chains - sick to death of pizza express.