What could have been done differently here?

The boy was shot at a point blank range. From that distance the cop could have just jumped on him and tackeled him to the floor. Or if he had to shoot, may be he should have shot him on this legs. But shooting a 12 yrs twice is cowardice.

dispatcher is supposed to be blamed

Are you guys serious? You wouldn't have said that if that gun was real and one of those cops was killed by that boy. Many cops are being killed every year by criminals every year and you hear nothing and when a cop killed a thug then there is a issue?. Bravo.
These cops aren't getting six figure salaries like some of you do where you just sit back in heated chair and just criticize their actions and it's not like they like to kill people.
Everytime they encounter a situation like this it's a intense moment and they know they may also get killed.

I want to ask you a simple question.
What would you do if you have gun and someone with gun/knife comes to you and tries to hurt you?
Would you use your special Martial art Kung fu technique to defend to make sure he won't die or just shoot to defend yourself?. Give me a honest opinion.

They won't give you any opinion, let alone honest one. They will wait till thing gets over and make comments like cops should have done this and that. Put yourself in that intense situation and think again.

This is fault of police dispatcher. The caller who called 911 clearly said it might be a toy gun but dispatcher didnt even tell it to police. She just says there is boy with gun on park .