Thank you for your reply. I have noticed a few fancier restaraunts open on a Sunday at lunchtime. What I wasn't so sure about was whether their lunch time set menus applied to weekends as well? None of the websites made that clear. Could someone shed some light on this? A brasserie type setting is definitely not what I wanted for his special day. I'd rather spend a bit more but not ridiculously more if that makes sense? Thank you for the cake suggestion. I will definitely check out a local patisserie. Many thanks once again.

as noted above, cake delivey is not something commonly available from local bakeries. Normally, every neighborhood has one bakery open on Sunday morning; and you might want to just bring home a selection of fancy pastries instead of one cake if they don't have the type of cake you have in mind available. It would be fun to let the kids help you select.

But if you do want a fancy cake on a Sunday, though, you can take the métro to one of the grand dept stores (now open on Sundays) where their upscale food halls do have ready made beautiful fancy cakes available every day including Sundays. (I particularly love the bakery section of La Grande Épicerie at Le Bon Marché. You can also buy many very fancy already prepared dishes there if you want to eat at the apt.

(we often bring dinner home from there if we have not had time to cook; so convenient now to have it open on Sundays!)

If you want a really nice restaurant for dinner which is open on Sunday and will be informal enough for the kids as well, I would recommend La Rôtisserie de l'Argent, which is an annex of La Tour d'Argent: https:/…

(easy to get to from where you will be) Perhaps the kids can share a main course, if you want to keep the cost down; the portions at this restaurant are unusally large for Paris (many people do take home "doggie bags" from here, which is not as common elsewhere in Paris)

Sorry, I just realized you wanted a recommendation for lunch and not dinner on Sunday. But La Rôtisserie d'Argent is also open for Sunday lunch. The website has the option to switch to English so you can see the menu; but I was thinking the children might enjoy sharing a roast chicken (you see them cooking on spits in the open kitchen: chickens and ducks are their specialities) & potatoes of some type. This will not be like any roast chicken you have ever had at home, not fussy but amazingly delicious.

If you prefer a local brasserie or café, I suppose suggestions would depend on whether you want to stay in your own neighborhood or go to another part of Paris.

Every restaurant (or café or brasserie) will have a menu posted outside, so you can also just decide which neighborhood you want to be in for lunch and check the menu of any place that looks interesting before you go in. If you are staying in a rented apt., it is usual for the owner to leave a list of suggestions for that neighborhood. (This is when a hotel concierge or someone at reception can be very helpful to recommend local places that are not tourist traps.) You can also find some very good recommendations if you browse through Trip Advisor reviews or La Forchette (The Fork). There is also a good website called Paris By Mouth which reviews restaurants: www.parisbymouth.com

Bon appétit.

LovesSunnyIsles thank you very much for your very helpful suggestions. Going to the department stores food hall may just be the thing! And thank you for the restaraunt recommendations. I will certainly look into it as well as the website for food reviews! :)

Le Train Bleu is a stunning restaurant. Menus used to be 40€ for adults. Kid menus were cheaper and just 1/2 portions of the adult menu, so very good. This may have changed.

Deliveroo delivers desserts, but the offers vary by date/time/neighborhood so you'd have to do a test run 2wks or so before the big day.

I was going to mention the lovely Train Bleu, as phread did, and also the iconic Bofinger, with its gorgeous Belle Epoque decor. I've dined in both with grandchildren, and both were very accommodating and welcoming. My most recent experience was at Bofinger when kids were 4,6,8,and 11. They had children's menus. And within your budget.

www.le-train-bleu.com

www.bofingerparis.com

Many many many bakeries are open on Sunday morning. Figure out which ones are in your neighborhood and then check out their cakes. some bakeries specialize in fancy cakes but most have pretty good grand pastries for serving 4-8 people. There was a bakery near the apartment we use in the 13th that a two block long line Sunday morning as people picked up magnificent cakes that they were known for. So finding a cake that looks intriguing and ordering it ahead should be easy; then you can just pick it up that day.

Fancy and 50 Euro don't go together very often. Bofinger and Tren Bleu are both great with kids because the rooms are so pretty. Food is fine and they are probably within budget.