"Umm aside" not-aside, I'm sorry for triggering you. it's too late for me to edit my comment and take that out but I would if I could. So this may not be obvious to you, but what's obvious to someone isn't necessarily obvious to other people, and vice versa. In any case, I can see why creating a separate account if you only have toddlers seems too onerous. Don't worry though, they'll become teenagers who want (and deserve) the autonomy and agency of having their own account before you know it, even if sharing your photos to their idevice wasn't enough to motivate you. Separate accounts seems the most reasonably way do implement a shared but-not-system to preserve privacy, a favorite reason Apple cites as their reason for doing things. I'm not sure how else Apple could do a shared system for teens.
I think there's a hack involving getting a cheap phone number for each toddler, adding that to iCloud, then disabling message delivery to that number but I haven't tested it.
I'm in agreement that Apple does not know how ipads are actually used in many families. There is nothing personal or private on our shared ipads, either, and it makes no sense to tightly bind each physical device to a single person's appleid. They are basically roaming web browsers and game screens. Nobody reads their email on them, for example. And this doesn't even get into the question of whether a small child should need to remember usernames and passwords and consent to EULAs. The devices should have settings which respect that while some individual's appleid (e.g. mine) is ultimately responsible for the device, that in no way reflects who the typical user of the device is or what they should have access to in the corresponding apple account. A checkbox during setup that says "this is a shared device that should not have access to my personal data" would be perfectly fine.
I think there's a hack involving getting a cheap phone number for each toddler, adding that to iCloud, then disabling message delivery to that number but I haven't tested it.