I think the same applies not so much to too many but too much work in the sense of sit down and think about what it is that puts the stress over the top - is it the child that cries too much, the child that demands too much, the parent that is inconsistent, the child that seems to be busier than the rest of the group and stirs them up, the child that doesn't fit in age wise - some little some older and an odd age in between that doesn't fit with either group, etc. Once you have identified what it is that is leading to the stress decide your options.

It won't be that you have taken on too many kids - it will be that you have taken on the wrong group of kids/parents.

Once you have identified the stressor look at making changes that will help such as simplifying routines, changing program expectations, speaking with the parent about the issue, and ultimately releasing the stressor and repacing them with someone that better fits with the group.