Try this:
NILF Training.
It should be an article on training method of "Nothing in Life for Free". This is a very gentle way of constantly reminding your dog that you are the leader of the pack. It works, too.
I would also suggest to constantly supervise your 3 year old and your little dog. My son was 10 and still putting his face up in Ringo's face (our Westie). I would constantly have to remind him not to do that. Heck, he's 15 now and I still find myself telling him . . No Face in Face!!! Ringo sometimes likes it and sometimes doesn't and gives a little warning growl but still . .
We had an elderly, geriatric Maltese when my son was 3 and although he was very gentle with him; he would still accidently step on his tail, stumble over him; etc. So . .watch then closely.
I agree that a trainer may be in order if you can't 'nip this in the bud' so to speak.