Places to eat with kids - Paris and Strasbourg

Edit: Just reread your post that your daughters aren't picky. This will be fun then.

Traveling with my picky 9-year old granddaughter in Paris, we have a reservation for a Breizh Café, several scattered around the city. The galettes tend to be inventive, but Breizh Cafe takes reservations and we're a group of grandparents, parents and kids.
Omlettes are on the agenda, and I figured my granddaughter would find something she likes if we go to Chartier at its opening hour. The huge menu has everything. It's not fine food, but old-fashion meat in sauces, etc.
We're also going to the Grande Mosquée de Paris for North African meal.

And I've just added something from Tocard's pizza suggestion to replace one of our crepe outings.

Otherwise, you'll find quality shops, especially in your neighborhood, the 7th. It's upscale neighborhood, so the shops carry nice products.

In France, children generally eat what the adults eat, so not sure how kid food would apply here.

Sounds like your family prefers carbs and simplicity. Why bother with restaurants? Stick to cafés and crêperies. Suitable locations are all over the city, but the high concentration of crêperie options is on rue d´Odessa and rue du Montparnasse just to the east of Montparnasse in the 14th.

If your family likes pizza, the best is Peppe Pizzeria. It's probably too late for July dinner reservations (generally a 2-month wait), but you might be able to reserve for lunch. The family might prefer atmosphere to other culinary parameters, try Pink Mamas. Book now for a July reservation. The kids will definitely love it.

Check out "Les Frenchies" You Tube channel for dozens of short (10-12 minute) videos on all kinds of places to eat in or take out in Paris. I think that they have a couple especially geared to children.
They have really solid, practical information and are charming to watch as well.

I am a big fan of the bouillons like Bouillon Chartier or Pigalle when traveling with kids. Big menu of French standards and very cheap. So you don't wince when a kid ends up not loving what they ordered. Plenty of kid choices like roast chicken, hot dogs, steak and fries etc as well as standard French fair like beouf burguignon or choucrout garnie or snails. And lots of classic desserts. AND cheap so a good place to adventure. The one in Montparnasse has a gorgeous room as do all the Chartiers. The Pigalle is more plain but has good food of its class i.e. lots of cheap options.

Crepe restaurants are also good with so many options of both dinner and dessert crepes. They are also on the inexpensive side.

There's a French restaurant chain called Hippopotamus which promotes itself as an informal meal with kids.

Another alternative in both cities is Flam's, which specialises in "flammekueche", which are Alsatian pizza with very thin and crispy bases.

Most cafés will have kid-friendly options… hamburgers, french fries, Croque Monsieur (basically grilled ham & cheese), soups, pasta, salads, bread & cheese, omelettes, etc.

Menus are always displayed outside so you can look before sitting. At a café, you can seat yourself anywhere if you want food… if you only want something to drink, sit anywhere that isn’t set for eating (tablecloth/placemat, napkin, utensils).

I would echo Philip’s rec of Hippopotamus. Kids love it.

My French godfather used to love Hippopotamus- and took us there often - in OUR FIFTIES lololol - I think it was fine - sort of like a Whitespot or nicer Denny’s lol

I also recommend the chain restaurant Leon de Bruxelles ( it’s a Belgian chain ) yes it features mussels - but has other options, and a child’s menu - and it’s air conditioned lol - there is one on Boulevard st Germain so likely could
Walk to it . Google for menu to check it out .

Ps the curry mussels were amazing - i had those - hubby had the ones done au gratin and they were good but we both agree the steamed ones were better ( they have a choice of many flavours)

In Strasbourg your kids may like tarte flambée, cousin to the pizza. No tomato or sausage; lots of creme fraiche, onions and tangy bacon on a thin crust. I don't know if it is ever actually set afire intentionally but the results are both pleasing and (relatively) cheap. If they hesitate, look around to see one being served because they even look worth trying.