Autonomy and Free Will off does not mean that the sims will stand there doing nothing if their needs are met. There is actually no way to accomplish exactly that in TS3. They're probably not going to get it into their heads to start a new project (painting, write a book, learn a new recipe, etc.) all on their own like that but they are still going to pet the dog, look out of the window, chat with each other, admire or complain about their own surroundings, etc. With NRaas StoryProgression one can arrange Stasis for sims, that's close but it does keep their needs maxed out 100% of the time and makes sims kind of boring to play and be around. But even then they will do things of their own accord occasionally.
Some of what prompts sims to pick up babies and toddlers (and pets) might be trait related, but some sims will just do that for no apparent reason. One thing that might help in such situations is issuing an NRaas DebugEnabler object reset on the sims so you don't have to make the toddlers active to cancel an action that may not cancel anyway; it's a very gentle kind of reset that merely force-clears the sim's action queue but it doesn't send them home/off the screen or do much else to them.
But that's not really going to cause your sims to stand still doing nothing waiting for a command at all times. The only 100% effective way to do that is to give them some random animation to do repeatedly by using NRaas Animator or a pose player.
