Do you like saurkraut? That might add some variety will still letting you eat cabbage, and the fermentation gets you probiotics, which are great for your gut. Other than that, I'm not totally sure, as I don't really eat much cabbage. That said, from the look of the nutrition facts for cabbage, there doesn't appear to be anything that you could potentially overdose on (it has very little Vitamin A, so you're not in much, if any, danger of turning orange, or overdosing on Vitamin A or its precursors; and it's not really possible to OD on Vitamin C, but at 1000g or more a day, you can rest assured that you're getting enough at around 500% RDV ), so I doubt there's really such thing as "too much," except if it's pushing out other foods (which it might be, 1,200g of cabbage is only about 300 calories, so if it's filling you up, you might want to cut back on it some in favor of more calorie-dense foods, at least until you get everything balanced).

As for being judged -- you're a parent, and you're Paleo. I hate to say it, but it's bound to happen sooner or later. Put your big boy panties on, arm yourself with information, and deal with it as it comes. Since you're tracking, try to keep track of the amount of Calcium and Vitamin D you're getting. If you're son and wife are eating the same, then you can show that they're in no danger of lack of calcium by dropping milk (and in fact, Dr. Cordain posits that even at lower levels of calcium in a Paleo diet, absorption is better due to higher levels of D3 and fewer calcium-binding agents, making each bit of calcium that much more valuable). And if he's going full Paleo, too, don't worry about your son being fat -- he won't be for long (seriously, boys, especially adolescents, seem to do especially well on Paleo when it comes to dropping body fat -- you might have to add milk back into his diet at some point solely to keep some weight on him (I suspect the uniquely high insulinogenic effect of milk and the IGF-1 stimulation it does has a lot to do with that as a "remedy")), and the naysayers about his dietary fat intake can stick that in their pipes and smoke it.

And fiber? Hell, your cabbage intake alone probably blows most people's fiber intake out of the water (1,200g has 31g of fiber), and it's the type of fiber your body can actually use, not the kind that is basically just poop inflaters.

I think the biggest concern will be making sure your son gets enough calories and the right balance for him. As a growing kid, he needs it. That may mean including a serving of sweet potatoes or some such, even if it's not something you'd eat. He can deal with higher carbs than you, especially if he's active (which he likely will be, even if he's not now). While you transition, it might help to at least make sure the cereal is gluten free. That way, even though you're still making a concession, it's the lesser of the evils of cereal.

So, what is it, exactly, that you're afraid of for your family? Missing nutrients? If I didn't already cover anything, mention it and we can help you make sure you're including the foods that have it.

Or are you just fearing judgement? If that's the case, it's no reason to quit Paleo. Arm yourself with knowledge of the likely arguments, and research the ones you're confronted with, when you're confronted with them.

What I've read from primal parents is how important it is to let kids have variety to choose their own carb/protein/fat balance. They tend to need a lot more carbs than the average adult, so putting out a bowl of berries or melons or other fruit every meal is ideal.

I don't think I'd eat 10 lbs of anything in a week, except maybe beef. You can't get ideal nutrition from eating so much of one food. Collard greens are great boiled with pork. Kale chips. Sauteed spinach with garlic. Variety is key! (and plenty of fat)

It's okay not to have all of the answers upfront, it can be trial and error, but the more you research, the more you know what's working and what isn't. Just keep an eye on your kid and don't let this way of eating turn into an obsession. Kids are impressionable. I would also suggest that you become familiar with the science, which would strengthen your understanding. Primal Blueprint is a really good book that helped me greatly!

You're way overthinking this

Put a hunk of fatty meat on the table, a few different vegetables, and berries for dessert. Keep some raw veggies & nuts around to snack on if you get hungry.

Mix it up!

Then you'll be fine No one eats perfect nutrition and I'm not sure that's even a good goal to fit your nutrition exactly to the average macros.