For food halls, there is the new Galerie Lafayette in Champs Elysee. Note that the food hall in Galerie Lafayette in the Opera district (Haussmann) has little seatings.
You can try Eataly too in the the 4th district in le Marais.
For crêperies, you can have a look at Breizh Café, they have opened new ones recently. Please note that you need reservation.
Since you are in Paris, it will be the best to try some bistrots or brasseries with kids, they usually have some steak or even kids menu. How about testing with Bouillon Pigalle, Bouillon Julien or Bouillon chartier? To see if they like French food, places won’t break the bank.
Kids usually like sweets, you can bring them to the tea room of Laduree!
As for bistrots for family, I’ll think about that and get back to you…