Upload & Sell: Off
I photographed my friends' kids growing up over the past 10 or so years and over that time my equipment has evolved somewhat. I've found I predominantly used 50mm, 85mm and 16-35 for wider, more environmental images. For a while I also used the 35 f/2, 24 TS-E and 45 TS-E, and not just because of the tilt function, but because of the nicer background rendering vs. the zoom.
The Canon 50 I currently use is the f/1.2L. As you've noted, it's a lens that people seem to either love or hate. I love it. Initially I didn't like it, because I was expecting it to be a 50mm version of the 85L, which it isn't. It's not as sharp at close portrait distances, but still plenty sharp, and for portraits it's also not necessarily a bad thing. This lens is under corrected for spherical aberration, which means the closer you focus, the slightly softer the image will be wide open. And, as you stop down, the focus will shift a bit away from the camera. But if you only shoot at or very near wide open, focus shift won't be a factor. While the lens has quirks, I find the images from it have a pleasing, lush quality. It's a bit difficult to describe.
I also own the 50 f/1.4 and have done side by side comparisons. There are differences in the final image, but minor. Notably the 50L does blur the background a bit more at equivalent apertures. The biggest difference though, IMO, is the 50L exhibits better AF consistency from shot to shot, which when following a toddler around, or young kids, can make a difference.
As for the 35L... there probably will be a new one coming, but with Canon's recent product pricing history, it will likely be in the near $2000 range. I'd just buy a used one for around $1000-1100 (lensrentals just had one listed for $1090, but already sold) and not worry about it, since that price should hold pretty steady even if a new one is announced soon.
I think 24 and wider can work for kids, but more for environmental vs. portrait shots. It will really depend a lot on how you arrange compositions and where in the frame the subject will be placed. Lately I've been favoring 28mm a lot, and also 21.
For example, here is 21mm on full frame at this lens's minimum focusing distance... You'll have to pardon me as it's not Canon gear, rather, the Leica 21mm f/1.4 M mount, at f/1.4. About its biggest drawback, other than price, is the 70cm minimum focusing distance, which for this kind of lens, is very far away. If there is a benefit, it's that distortion is less of an issue simply because you can't get crazy close with it. I think you can get a fairly good idea of what the 24 f/1.4L would give you in comparison - a slightly tighter crop and a touch more background blur:
And not quite so close:
After doing this casually for a number of years, I find that a combo of ~20/28/50 is a good range. But 28mm is kind of a dead zone for Canon since the 28 f/1.8 isn't highly regarded (I haven't used it and therefore won't comment further). While 85 is a great portrait lens, I find I usually work pretty close with younger kids and it's actually too long many times, thus 50mm has become my 'blow out the background' portrait lens.