That's cool. You should post a video to show off your fancy button / light setup!
Rather than training you might just want to work on choosing a phrase that works for your son. Generally a trained profile is only really useful for one person so unless you want to have a special profile just for him the training is likely to cause problems for you in general. It is also important that he understands how to talk to a computer (something many new VC users of all ages have trouble with!). You need a silence before your command, and then you need to say the correct phrase clearly. Consider it an opportunity to get him started on good diction early in life.
That said, if you right-click on a command in the tree editor you can train with that 1 command by selecting "Train speech profile" from the context menu, or you can select a command and press Ctrl-T on your keyboard. You should start with the rejection level quite high and lower it until accepts the command. There is also an action for switching between speech profiles so it could switch to his profile when he triggers the motion sensor in the morning.
I don't actually know how well it will work for you but you can give it a go and let us know!