They were loitering in the hallway with ballistic shields that would stop a proper .30-06

No they did not. They had Level IIIA shields. They are rated for pistol rounds.

That it worked eventually says it would have worked before more children died.

No it does not. You have no idea what the police had learned by that time that they didn't know to begin with. The gunman was probably calmed down. He may have been ready to give himself up for all we know. They may have had a means of seeing what he was doing by that point.

The bottom line on this is from outside in the corridor all the cops knew is they had an active shooter that was probably using multiple children as a human shield and had the entrance door covered by rifle fire. Only ape level intelligence would think the local cops should try to go running in there shooting. It is the same level of intelligence that tried to force vaccines, that claimed Jan 06 was insurrection, that BLM was peaceful protest. Complete fucking nonsense.