Couldn't we just leave them with lower elementary school teachers?

I understand that lower elementary students currently go home after school around 1:00 PM. Instead of that, couldn't we have the elementary school teachers stay for just two more hours until 3:00 PM to supervise classes or playtime?
Since almost all parents are dual-income nowadays, this would reduce the burden on parents, and more importantly, children would be safely protected within the school fence. Isn't that killing two birds with one stone?
Even for elementary school teachers, 3:00 PM is a very early finish compared to the typical 6:00 PM workday, so I don't see any reason to oppose this.