Here are my random and poorly put together thoughts.
1) if the kids are moving, the AF might be nice. You had the F90x, so you should know what you are missing if you go all manual, though. I would have suggested an N90 or N90s, as they are pretty cheap these days.
2) The next toy I would have recommended was the OM-1. My first camera, and I loved it. As you note, they are cheap now. The one drawback I saw was that there wasn't the whole stable of glass as for the nikons. E.g. there isn't as much in wide angle. Reasonably light.
3) A MF Nikon. If you go back to the AF, then you can use the glass for both. I have the N90 and an FE. The FE is a bit bigger and heavier than the OM, but not that much. The 100mm 2.8 Series E is light, cheap and good. All the older manual focus lenses are available at reasonable prices.
4) The Canonet is a great toy. I used to keep mine loaded with 3200 speed film. It is quiet and has good glass. I got a lot of shots that no one saw/heard because it is quiet. However, it isn't really that much smaller than an OM1 with a 50mm lens.