Just my opinion, so take it with a grain of salt, but there are 2 issues going on here.
First is you have a baby that you are asking a ton out of as far as obedience. I don't even START 'real' obedience until around 6 months old. Not that we don't 'play' obedience. It's all just a big game with the 'sit', 'stay', 'come' etc. With tons of treats and toys and fun fun fun. So my dogs just LOVE all these 'games' and think it fabulous! So exciting for my dogs to train, I don't 'make' them do anything they do it fun and fast cause it's such a blast for them.
What I DO do with my dogs the first 6 months is what I see as your second problem. SOCIALIZATION!!!!!! That's my main goal and aim in life. To raise happy confident pups that, as adults, are confident in ANY situation. I think you have hit the nail on the head, your puppy isn't protecting you (they aren't old enough for 'real' judgement decisions in protection) he's terrified!
I've had friends with similiar problems because they wanted to train their puppies BEFORE bringing them out in public. Didn't want to be embarrassed by a dog that wasn't behaving. So they did all this 'training' while unintentionally also isolating the pup from the VITAL socialization they need the first year. Our pups go thru stages the first year in particular that, when we miss them, we can NOT get them back to do as well as we could have. Not saying we can't fix some of it, but not as well as if it's started from the day the puppy is born (really, it even matters how wonderful the bitch is to how wonderful the pups are!!!).
I believe your puppy is afraid, and if they bark/growl it keeps the scary stuff back and away so they can feel more comfortable. So it's all from fear, though it looks like something else.
What I do with puppies is socialize the heck out of them so they realize the world is a wonderful happy place with many glorious things in it, and they can look TO ME for guidance and leadership as we wander through it. So my pups know I will deal with scary thing so they don't have to panic and overreact by having to bark/growl to keep it away. Either it's not scary at all (look at mom, I'm happy). Or it may be something to be careful about but mom will take care of it (look at mom, she's in front of me and blocking away the scary thing).
I love puppy classes before 6 months because they show a better balance on the low levels of training we should expect out of such a young puppy AND have a huge level of play and socialization in a safe environment for the pup. So that when I DO start up 'real' obedience at 6 months it's with a confident happy puppy who is able to focus and listen to me in a room full of other dogs and handlers cause it's just another day out with me!
Here's some sites that talk about socialization, fear stages, and expectations we should have for our puppies: