We went to a few restaurants in the marais with the kids, can't remember offhand, so will have to ask my sis for reminder. But in general, all restaurants were v child friendly (even if it didn't look like it). Food wise don't know about fishfingers but 'croque monsieur/madame' (cheese (/and ham) on toast) and frites always seems to work. All the bistros will sell it.
Quite nice to sit outside by the Pompidou. if you go to the rhs, there's the fountains with all the colourful Nikki St Phalle kinetic water sculptures - lots of bistros here.
Also nice bistros and cafes in the Tuilleries gardens - don't know how old your kids are, but it allows you to sit outside to eat/have coffee and they can run about. There's also carousels and trampolines!!
If you have time for child free cocktails either: China Club (between bastille and marais)
50 rue de Charenton, 12th
"With its huge chesterfields, low lighting and a sexy long bar, it?s impossible not to feel glamorous here. They take their Martinis seriously, and their well-made champagne cocktails."
or 'le Fumoir' - very cool nd you can sit and look over to the louvre.
- Le Baron Rouge
- 1 rue Théophile-Roussel, 12th (next to bastille market)
fab, very french wine bar (also serves oysters sunday morn) everyone drinking wine and oysters out in the street using car bonnets as table tops - so long as it's an oyster month (has an 'r' in it)
Le Square Trousseau
1 rue Antoine-Vollon, 12th
lovely restaurant - v. friendly and good food
Hope that gives you a few pointers, even if they're not specifically child orientated.