Martin has been paying very close attention to Lana and Zach.
He has a great time playing with his older sisters, but he has decided that he needs a younger brother with whom he can get into more boy-like mischief.
So, he has figured it is never too late to start the training regime.
Here he is showing Zach the approved method for holding a toy gun.
Considering that Zach is still at the stage of accidently discovering that the things at the end of his arms are actually under his control, this training may be a bit premature.