I cannot recommend any specific shops but do echo another reply, visit Monoprix's food floor ( in many Monoprix the food shop is on another floor) and look through the goodies. Some of the best chocolate I have had is actually baking chocolate or meant to make dessert out if it. I think it is Nestle brand, in a large bar meant to be melted into dessert. The caramel chocolate is so delish. The candies and chocolates are so interesting. I like the European Nutella better than the North American, less sugar but still sweet, so delicious. I have heard that the candy brand Haribo is made in France (not sure of this); you should be able to find it in a regular grocery store like Monoprix or Franprix.
I also suggest observing where the longest lines are in bakeries you pass. Join the long line and observe what pastries are purchased by others. The children could pick out 1 or 2 for themselves, then eat it in a nearby park.
There are often crepe vendors selling them from a window in a shop along the street. I cannot eat wheat, but that would be a nice lunch or dessert or snack at any time of day.
I do love the outdoor food markets where there are veggies, fruits, cheese, meat, some cooked food like paella and the rotisserie chickens. I had a great ham cooked in grainy mustard and scalloped like potatoes from the Grenelle market on year; we took our purchases to the nearby Seine, found a bench and chowed down. Such a wonderful memory. Use google to find the open air food markets in Paris; there are many official Paris websites listing them with the days. My faves are the Grenelle at the Motte-Piquet-Grenelle Metro stop; that market runs underneath the metro that goes above ground for a while. 2 days a week (sorry, cannot remember which days). Another favorite is the President Wilson market, near the Iena metro stop; this one is a bit richer but busy with a variety of things to see like handmade soap, fabulous knit scarves, regular scarves, flowers, and food. Buy some cheese from the busiest booth, some bread, purchase a small knife somewhere (Monoprix) and have a great picnic. Add some fruit and veggies, what a great meal. There are so many markets. i am not sure where you are staying; a hotelier can advise. Markets are an inexpensive way to purchase fresh and fabulous food.
I would also recommend going to the grocery store (Monoprix is my favorite) and peruse the yogurt aisle. It is a wonder in itself. I usually purchase some chocolate mousse disguised as yogurt. The selection is unbelievable. I might take 10 minutes to decide just staring at all the choices. Try some different flavours like fig. Fig jam is also a great buy at the grocery store.
I advise finding David Lebovitz online; he is an American chef now living in Paris. He has a great blog/website with many foodie recommendations. He has a way with words. He loves to go to markets so he has a number of blog posts about his finds there. He also reviews some restaurants, with varying price points.
My mouth is watering. Enjoy Paris. SO much food, so many markets.......