This is butterfly wings nonsense. Not nonsense in that events have have unpredictable consequences, but nonsense in that we should allegedly suppose every positive act to assist the future should be presupposed to engender the worst consequences imaginable. This is hopelessly flawed, because NOT acting could also doom the universe!
There are no good consequences in the scenario, either a little boy drowns or another child's existence is deleted (and it was your scenario). The point being, no matter how much Spock may try to assist in mitigating the damage... people are still going to die.
Should he tell the Federation about the Organians? So they can make sure they steer clear and can fight an all-out war with the Klingons and millions can die?
You can play 'What If?' til the cows come home. But if Spock misplays his cards or misremembers a key event, he could bring an even worse Hell down on the Federation.