I don't think a mod like that exists, although I wish it did. I've looked everywhere for it too. I've tried using MCCC to turnoff the autonomy for "ask to be let out" on the high chair, but it didn't work. You can also kind of fix it by locking the door for everyone when the toddler is in the high chair. If no adults can get into the room, the toddler won't call for anyone and they will just magically pop out of their high chair. I know this isn't what you want though. I hope someone else can find a better solution.