It would be useful to let your son be "the keeper of good things" with regards to Lex. Have him feed Lex, give him treats (only when Lex is being well-behaved, of course), let him be the one to give him new toys, etc.
If Lex knows any commands like sit, have your son give Lex commands periodically (which naturally are always rewarded with a treat!). Your son and Lex will need your help. If Lex hasn't been taught to obey commands from your son, he probably won't understand what is happening at first.
If this type of behavior escalates, I would definitely consult a positive trainer.
Good luck!
__________________  FirstYorkie
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