Thank you to all of you who gave advice. We went, we spent, and we ate!
We followed much of your advice - within hours of arriving we'd walked to the Rue de Montregueil and eaten our way through an alarming amount of euros -we bought a set breakfast in a cafe just to get our bearings (coffee, juice and croissants). Once the market was fully open we had a ball, the 13 yr old went mad buying chocolates - only 70% cocoa solids will do for him - it was Easter week and all the Chocolatiers were showing off their best! We bought fab bread and sublime cheeses - the mixed plates of cheese were probably the best value buys of our whole month away. We bought bread from artisanal bakeries. Ate lots of pastries of course and shopped in charcuteries, fromageries, and vegetable shops. Bought things like yogurt to go with our strawberries in the little supermarkets but most else we bought from specialist shops.
We ate and drank standing up in all sorts of interesting cafes. Had crepes in a restaurant full of French famillies.
We bought wonderful sandwiches to eat at Eurodisney so avoided buying nasty pseudofood. (the kids re named it queue slow disney - even they got fed up).
We had an excellent dinner in Les Juvenilles as recomended and we were staying in the same street - it was extravagant for us but the food and wine were very good and by then we were very grateful for an english speaking waitress. Pity the restaurant was being monopolised by a very drunk group from the US but it was the only time we ate anywhere with other english speakers.
We got by on high school french, mime and good manners. and everyone was helpful. We ate in a brasserie in St Germain??(i think) - ordering variations of the set menu as suggested - entree and main or main and dessert - My boy ate his first Creme Brulee on a spring evening in Paris !!!- we are so blessed!
We walked everywhere so burned a lot of calories. Even ended up eating in the cafeteria at the louvre as someone suggested.- when it was pouring with rain. Never made it to the Gallery LaFayette as simply not enough time but we really had a great time.
I am so grateful to all who made suggestions as I was much more confident and able to say NO! when the 16 yr old wanted to gravitate towards starbucks simply because it was familliar.
I'd go back to Paris in a heartbeat, (next time without the teenagers!) Merci mon amis.