I've never had toddlers be
that hard to take care of. So it's possible you're experiencing a bug. Looks like there are a couple reports of bugged toddler interactions, you might check those out and see if they sound similar:
https://answers.ea.com/t5/Bug-Reports/NEEDS-SAVES-My-sims-won-t-take-care-of-their-toddler/td-p/9418528https://answers.ea.com/t5/Bug-Reports/OPEN-Toddlers-can-t-be-put-to-bed-read-to-sleep/td-p/8142086If it's not a bug, some other things to check:
Toddler traits matter a lot in how they behave. "Independent", and "wild" toddlers are the least cooperative, I've noticed in my games. It can be very hard to get them to do what you want them to do. Locking the door to the room helps keep them from queuing up some other activity elsewhere on the lot and makes them (and their parents) a little more manageable.
Dragging food directly in the toddler's inventory and then directing to them to eat it from there sometimes works better than putting it down somewhere and sending them to eat it.
Have you tried turning off autonomy completely for all sims in your household? If you try that and they
still cancel your commands, there is probably either a routing issue or a bug.
If you are okay with cheats, you can use "testing cheats on" and then shift+click on each sim and choose "make happy" to restore their needs and give you a chance to figure out what's going wrong before someone dies or gets taken away.