Did you pick up from the playground? Is your daughter one of the last kids picked up?
Many centers combine all classes, of the latest pick-ups, to one playground to save payroll expenses. The classrooms are then cleaned and full-time staff sent home.
Typically the staff to stay with the last combined group are the part-time teens who come in after school. They receive the kids changed and ready to go home from their usual teacher at the end of their shift. Finding out your childs teachers schedules can help prevent issues like this in the future.
Toddlers like to toss mulch over their backs, it is a constant battle. As they bend down, the diaper gaps in the back. "No throwing mulch" is an afternoon mantra in many centers.
Try a onsie under clothing for a while.