Hi Steve,
The website where you manage your children's access to content will be the same for Windows 10 and previous versions - account.microsoft.com/family. The difference is that when you have Windows 10 devices (including those that have been upgraded) any settings that you set for the MSA that your child has will be able to be applied to *all* of those connected devices.
For those devices that aren't upgraded, the steps to get set up are nearly exactly the same as they've been - you'll need to set up each child on every device, and then you can still change the settings online. Each non-Windows 10 device will have a separate report, though, so if you have 3 children on four devices, you'll get twelve activity reports (but if two PCs were upgraded, that number would reduce to eight, because the Windows 10 ones would share that roaming goodness, and if all four were upgraded, you'd be down to just three).
As for the settings being able to be customized by device -
I get what you're saying - on a shared computer, maybe there is a desire for more stringency. Hopefully you'll find that with the simplified settings toggles (as long as you scroll DOWN on the pages!) will help make sure our kids are safe regardless of the devices they've got access to.