My littlest guy is vegetarian (by my choice, except he takes CLO so I guess not technically, but he eats no other animal products), eggs free, animal milk (he does human milk) free, wheat free, corn free, soy free & a couple other fruits and veggies-free (by necessity of allergies/intolerances). He is also nut free as of right now. My DH and oldest little eat everything under the sun, though mostly healthy stuff (mostly veggie with some dairy added or such) at home. I am veggie (except the CLO too), with raw vegan leanings, though by no means there yet. I am wheat free and mostly soy-free and avoiding milk/eggs products as much as I can, though am not terribly strict. It is an adventure cooking for everyone, to be sure, but we are mostly happy with the arrangement.
My littlest eats plenty and is a healthy little guy. He eats oats & rice for grains, potatoes, most fruits and veggies either raw or cooked (fruit dried too), legumes, seeds, lots of good fats (avocado, coconut meat/oil/milk, olive oil, olives etc). He drinks mama milk on demand and otherwise drinks water, rice milk in his cereal (rice chex) or oatmeals for bfasts. I make a lot of meals with rice and veggies and slightly alter the ingredients/add meat or dairy or eggs with it for the bigger guys....or legume dishes, which everyone likes (thankfully!), or say noodles with pesto and parm cheese for the big guys and rice noodles with pesto and nut. yeast for the little guy and a side they will all eat. I also use zuchinni sliced into very thin noodle-like strips (either raw or lightly cooked) for both of us (the big guys don't like it).
For baked goods I use: flour = oat flour, butter= coconut oil, sugar =apple juice concentrate, molassas, honey, maple syrup, agave nectar, or some combination thereof, eggs = ripe bananas....I make it work.
I like to make stuff we will ALL eat, like a vegan stirfry or curry with rice, muffins or bread we can all eat and all like, oatflour vegan pancakes, fried greens and hashrbowns, etc etc.
Hope this helps, in your place I would simply allow the sugar as long as it was in a form your child isn't allergic to (my little guy is intolerant of corn, so no corn syrup for him, YAAAY!
ETA: see that you asked for specific menu ideas...besides what I've already mentioned, some more ideas:
--Hummus and veggies, with fruit on the side...
--Veggie burgers (I have some good home made recipes, PM me if you want ideas) on a big salad, or just on a plate without a bun (I put all the fixin's on them anyway and just leave off the bun).
--Soups: we like split pea, veggie (I add beans for all, and noodles for the wheat eaters).
--Stuff on the grill is yummy: portabellas, zuchinnni, carrots, mushrooms, onions, peppers, eggplant, salad (yes, salad) etc. I like to lightly steam most veggies before putting them on, then marinate them in balsamic vinegar+ olive oil + garlic powder+ s&p, or a dressing we really like.
--If you guys do corn there is a whole world of corn products for ya...Corn torillas for tacos or veggie fajitas, corn bread, corn stuffing, mmm!
--Lentils with tomato paste, cumin and grilled/sauteed onions on top over rice or quinoa... lentils with 'stuffing' seasonings--sage and thyme (best in fall or winter) served with other cool-weather dishes like cranberry sauce, pumpkin/squash/sweet tato sides
--Pumpkin, sweet taters, squash cooked all ways. Sweet tater fries. Sweet tater pancakes. Steamed squash, grilled squash, baked squash (using a lil oil and diff spices makes for very diff tastes), squash soup.
--Broccoli with sauteed garlic in oil...
--Black beans with garlic, cumin, lime and coconut milk, SO GOOD.
--Soups, with or without bread/muffins from a gluten free grain.
--Rice noodles with sauce or stirfry or cassarole.
--Thai curry, indian curry, tomato & basil & garlic & nutritional yeast-based stirfry...pesto with whatever.
--We do oats so I make oat flour pizzas with flavorful satueed veggie toppings (mushrooms, onions, garlic, peppers, green or black or both olives, sauteed in olive oil) on top of sauce and nut. yeast (& cheese for the cheese eaters), YUM.
--Coleslaw with an oil base...
--Potato salad made with an oil based dressing instead of mayo...
One last trick is that when I make food that I know everyone likes, that heats up well the next day, I always make extra so that I can freeze some for later. There is a lentil or split pea Indian curry that I make that we LOVE, and I always make a huge vat of it (the biggest pot I own) then have leftovers the next day & freeze the rest in single-serve size in the freezer. Same thing with veggie burgers, pancakes, muffins/bread, split pea soup, etc)