I am kind of indifferent on Sunday School lessons for children under 3. Mainly they just need to be well cared for and if there is time/resources to do any "teaching" then that is fine.
More than anything I think you are too stretched with too little help. At the least, the babies (any non-walkers) should be in a separate room. I would also look into recruiting teens to help on a rotational basis. Can anyone help you with the room set up?
*I just noticed that you said you are there once a month, which might change things.