Well, if it were me I'd try really hard to make a lesson plan that fills up every moment of time! Its hard with such a range of ages, but I'd keep a list of simple things to engage them in and move from one thing to the next. Plan 5 minutes for each activity. Sing, story, make a craft, eat a snack, sing again, play ring around the rosie (you'll have to hold the baby for that) and son on. If you keep them occupied and busy the whole time, then they will not have time to fight.
Is there any way to divide the group by age? I think it would be helpful to have the under 2 yo. kids in a separate room from the older ones, and have a 2nd caregiver take one of the groups.