Sorry but going from being a Jedi to killing children because the Jedi council was not accommodating is just lazy writing..
I wasn't happy with the way the character progress (regress?) was handled but I think you are being a little disingenuous here. He does not "go to the dark side" because the Jedi Council wouldn't promote him to Master. By the time he is killing children, he has been thoroughly manipulated and brainwashed by the Emperor into believing that he will learn the secrets of cheating death. Anakin's central weaknesses are his attachment to others and his major insecurities about losing the people he loves. This is what Yoda picked up early on in TPM. The Emperor, as you know, exploits the hell out of this weakness and by the time he has struck down Mace Windu, there is no going back for Anakin. Cutting down children is just a means to an end.