Use 'run wild' to describe chaotic behavior, especially in groups or children. At the birthday party, the kids were allowed to run wild.
Pro Tip 2/3
Connotations of Disruption
'Run wild' implies disruption or lack of discipline, not just energetic activity. Without proper guidance, the students' discussion started to run wild.
Pro Tip 3/3
Negative Implication
The phrase often suggests a negative view of the uncontrolled behavior. He's been running wild ever since he stopped following his daily routine.