“Ummm” aside, this is not at all obvious. I have an iPad from before I had kids. When setting it up, I was asked to enter my Apple ID, so I did. Then came kids and a new use for this iPad, and a second iPad, which obviously needed the same apps, and a third. No, it never occurred to me to set up appleids specifically for toddlers. It did eventually prompt me to set up a new “iPads” appleid when I switched from android to iPhone and suddenly discovered that all my text messages were being delivered to my children. But the ipads are family devices, not per-child, and if apple thinks I’m going to give each kid an appleid, they aren’t paying attention to how people actually want to use their devices.

"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 still firmly of the opinion that Apple does not know how ipads are actually used in many families. There is nothing personal or private on our shared ipads, and it makes no sense to tightly bind each physical device to a single person's appleid. 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.

Not sure if you have kids, but the devices didn’t start out as being theirs. It was my iPad, they started using it more as they got older, and eventually I got a new one for me. I should set it up properly, but it happened gradually and I have not gotten around to changing it… and now all the apps and accounts and settings are tied to my Apple ID.

The more important question is how old are yours? Toddlers can't read so much, so it's easier to understand not making them their own accounts it a priority. On the other hand, if they're teenagers, seeing private texts between their parents could be deleterious to their mental health. Still, they're not getting younger. The only way out involves some level of pain, but the sooner they get their own accounts, the less pain there will be.