Considering the state of Cybertron and the Transformers race in the live-action series, being a Child Soldier is one of the least of their problems.
Keep in mind that pretty much all Cybertronians are millions of years old. Skids and Mudflap are likely just immature.
And the novelization of the third film has them killed by Sentinel Prime.
Compared to much of the other Transformers "universes", there is little talk in the films about energon, aside from a few references to "Energon Detectors" and as a replacement word for "blood". (i.e. no allusions to secret stashing of energon off Cybertron, the existance of natural sources of energon on Earth or even the manufacturing of synthetic Energon that dominated G1.) Starcream even mentions in Revenge of the Fallen that the Energon shortage is making reproduction impossible. Given that Cybertron is a dead world, and the only known remaining source of Energon is the Matrix of Leadership '' does this mean that aside from the 9 Autobots on we see in the film, the entire Autobot race is slowly starving to death?
Some fans might have been put off by how Optimus Prime killed Megatron in Dark of the Moon, because that is not how fans see Optimus. When you look over at Transformers: Prime, and see how Optimus was intent on killing Megatron after Raphael is nearly killed, the scene's brilliance comes into play. Because of Megatron's actions over the course of Revenge of the Fallen and Dark of the Moon, Megatron had gone too far in Optimus' eyes, just as his Transformers: Prime counterpart did.
On another side, considering that Optimus's master, Sentinel, teamed up with Megatron because he thought that the Autobots were never going to win, Optimus probably refused because then he would be no better than his master.