Injured while throwing beanbags... Lawsuit filed 2 years later

During an elementary school class
The teacher had the students play a game of throwing and catching beanbags
One student slipped and fell
They injured their patella and suffered a 6-week injury
Two years later, the parent filed a lawsuit against the teacher for professional negligence resulting in injury
Hmm... Why didn't they do it at the time and wait 2 years??