OP, just to say I know what you mean about needing to learn/understand your own specific dog's growl....we've had Mouse for about six weeks, and are still learning each others' communication techniques!
Also, he does definitely regard dd2 - the smallest human, and not much taller than him - in a slightly different way. I think he sees her as a weird fellow-pup, and less as one of the humans who feed and look after him.
This will change as she grows, so to some extent I just (try) implement caution around her, keeping close eye on cuddles etc, and she has learnt to sit at table or up at the breakfast bar to snack, rather than walking around with biscuits in her hand (great side effect of having a dog).
Also, do involve your ds in pup training...thats great...use treats, but do it with him so pup sees you and ds aligned together, as it were. I literally put food in mine/dd's hands together, but I also hand her the food bowl at meal times to give to him sometimes - so he associates her with humans rather than fellow pup.
No idea if any of that is accepted dog psychology, just seems common sense 
As for the poster who likes dogs being dogs and not dressed up accessories? Me, too - and part of dogs being dogs is that they do growl, they do have brains, and they do behave better when they are happy: like most animals.