Ah, the child actor. So much competition, so much drive, so many stage mothers and many others, as we shall see, pushing. Oh, and then having to survive the bad reviews. But when a child actor makes it big, there is lots of money and other perks to go around. They say for a child actor to succeed, they and everyone supporting them need to be ruthless. But ruthless to the point of killing a rival? For the lead role in the third-grade play? The center of attention in “Ruthless! The Musical” which is just ending its first week of sold-out and nearly sold-out shows at the Sacramento Theatre Company’s Pollock Stage is Tina Denmark. Right behind Tina is Sylvia St. Croix, child talent represent