I am not a professional photographer. I love taking pictures of my kids (candids/posed/indoors/out) and family and I also enjoy taking nature pictures (landscapes, flowers, scenery in general). My kids are 3,5, and 6 so we aren't quite yet into the realm of organize sports and the like, but perhaps someday!
Based upon your description...
Unless you want to make 4, 5 or 6 foot wide prints from your images, you really don't need a full frame camera. Yes, 5DII is good for about one more stop low light shooting than the current crop sensor cameras. But more recent crop cameras are also better at low light shooting than your venerable 30D. More on this below.
There are a number of excellent ultrawide zooms available for crop cameras. You are right that 28mm isn't very wide on them, so you simply need something wider... I use the Tokina 12-24/4 and think it's the best value. But there are other good options: Canon 10-22, Tokina 11-16/2.8, Sigma 8-16, Sigma 10-20 (two versions currently, I believe), Tamron 10-24. Some use Canon 16-35 or 17-40 or 17-55/2.8 and think those are wide enough (I sold 17-35/2.8L and replaced it with the 12-24.)
You also don't need the 7D. You'll end up paying a lot extra for pro-oriented features that you are unlikely to ever need or use. In addition, 7D is designed with fairly experienced photographers in mind, has less automation and requires more user input than most. It's the most pro-oriented 1.6X crop camera Canon has made, to date. It is not "right" for a lot of people... We see an awful lot of "help" posts here from people who bought it and are struggling to learn to use it well. I've been shooting for 30 years, much of it professionally and have used dozens of different cameras... Frankly, I found the 7D pretty hard to get up to speed with. After a couple months frustration I came close to sending back the pair of 7D I use and going back to using 50D. Finally, 7D are pretty heavy. They are noticeably heavier than 30/40/50D (which are all about the same), considerably heavier than 60D (which is lighter than the earlier xxD models), and even a wee bit heavier than full frame 5DII.
I'd suggest get the 50D... Or a 60D.
50D would be almost identical control layout to your 30D. It is an easy switch (I upgraded from 30D to 50D a while ago...it's a very nice upgrade... you'll love the self-cleaning sensor, all the additional image resolution, bigger LCD, etc.).
60D uses slightly different control layout, but the functions are still much what you're accustomed to with your 30D, so should be pretty easy to learn too.
50D is similar size/weight to your 30D.
60D is slightly smaller and lighter. 60D also has that cool articulated LCD (first Canon DSLR to have one... The T3i is the second). And it has a "locking" mode dial that's nice to prevent accidental changes (which can be retrofitted to 7D and 5DII too... but at a cost of $120 per camera).
50D is 15MP and 60D is 18MP... pretty similar. They also have pretty similar auto focus system and performance, similar frame rate (60D - 5.3 fps, 50D - 6.3 fps)... a lot of other similarities. With either one, you can interchange different focus screens (which you can't with your 30D). 50D has a good 35 zone metering system... 60D's is a newer 63 zone system that's now used in many models, but isn't really all that different in use (with my 7Ds, I think I see slightly better metering in tricky situations such as strongly backlit subjects... but not a dramatic difference by any means).
50D cannot shoot video, but it does have Micro Focus Adjust feature which allows you to fine tune your lenses on the camera, if you wish. 60D can shoot HD video, but doesn't have Micro Focus Adjust (IMO, Canon was dumb to leave it off this camera).
50D can be optionally fitted with a BG-E2N vertical/battery grip. That and the camera use BP511A batteries, which are widely available as cheap generics, same that you use now in your 30D. The grip is also interchangeably usable on 20, 30 and 40D. There was an earlier BG-E2, which is nearly identical. And, 50D uses Compact Flash memory cards, same as your 30D.
The 60D uses a new grip, BG-E9, and the newer type of LP-E6 batteries. These batteries are nice... long lasting, but they tend to cost more, though prices have come down a bit and some generics are now available. On the plus side, where I used to carry two backups for each BP511A in my cameras, I now only carry one backup for each LP-E6.
60D uses SD Memory Cards. So, CF memory you have for your 30D wouldn't work in it. But, depending upon the size and speed of that memory, you might want to upgrade even if you chose 50D instead. (For example I used 2GB memory cards, most 133X, with my 30D and earlier models... with 50D and later I switched to 8GB or larger, UDMA 300X and 400X).
60D is, of course, currently in production. 50D just recently was discontinued... It's a real bargain buying it refurbed from Canon store or through CLP. If possible, get it with 28-135 IS... That lens is really quite a value at the "kit" price... last time I looked at the refurbs/CLP, they were only charging $100 additional to add the lens! It and a wider one such as those I mentioned above might be all you need for a while. You may want a larger aperture prime lens for occasional portrait/low light, such as the entry-level Canon 50/1.8 or mid-grade 50/1.4... or a 28/1.8 or Sigma 30/1.4. When your kids are older, if they participate in field sports you might want a longer lens such as a 75-300, 70-200, 100-400, or one of several other possibilities.
You mention low light and using high ISO... for comparisons sake, we all have different opinion what's "acceptible" as far as high ISO noise and graininess... But with my 30D I tried not to go above ISO 800... would occasionally shoot 1600 but knew it would mean more post production work (from the RAW files). With 50D I never had much concern about using 1600, but tried not to use 3200 much. Now shooting with 7D, which are essentially same 18MP sensor as 60D, T3i and T2i, I'll use 3200 more often. I also shoot with 5DII and have no concern using it at 3200, occasionally use 6400.
So, the full frame camrea is still king of low light... In my opinion good for two or three stops higher ISO than 30D. 60D (and the other 18MP) are good for about two stops. 50D is good for about one stop higher ISO.
There are a number of improvements in softwares, too, handling noise. Both Lightroom 3 and Photoshop CS5 that I use are a great deal better at noise reduction than earlier versions. There are also more sophisticated, noise specific softwares you might try... and be able to push above the ISO levels I mentioned above. Or, just convert really high ISO images to black & white! That can look great... sort of like some of the great old high speed B&W films like Tri-X and HP5.
Have fun shopping!