When kids get sleepy, a number of things tend to happen at once.
For example, they might get more cranky, emotional, and impatient. And, if they’re engaging in physical activity, they also lose their balance easily. So, an ensuing fall further elevates level of crankiness creating a snowball effect of sorts.
Whenever I witness this, I am reminded of the power of interwoven complexity. It is hard to predict the behavior of complex systems because of the many interactions between the various components. If our human bodies alone are so complex, just imagine the futility of attempting to forecast short term stock market movements.
It is also a good reminder of the importance of getting sleep. It helps.