He never tries to achieve those dark side powers, he just receives the promise that he will. So no, killing children isn't a way to increase his dark side powers, is just a non sense attempt of showing a pissed off Anakin...

I think Anakin should kill Windu, or at least be passive in that aspect, then accept Palpatine's help as he's done things that he knows would have no return in the Order, so stays there with Palp, always with the hope of saving Padme. So he gets sent to Mustafar, and kills everybody... but the spirit should be he's doing it without anger, a feeling of a constricted person. Then fights Obi, gets chopped and Vadered up, he is told that all he's been through was pointless, and get this angry, lonely, condemned villain, move by the hate of himself... goes and wipes out the younglings... End of the movie (?).