No - I don't think you are worrying over nothing.
Freddie is growing up and that involves going through several developmental stages - including fearful. He's a confident little chap which is good. He's settled in and become one of the family and I'm a firm believer in start as you mean to go on. From day one of a new addition joining the household begin spelling out the rules and teaching what he is allowed to do and what he is not.
Nipping a potential problem in the bud is a darn site easier than dealing with trying to correct a nuisance problem which has become a habit.
As Michael said he is displaying normal puppy behaviour, but this doesn't necessarily mean that it is acceptable. It's normal for my dog to cock his leg - but he sure as hell aint doing it against my settee!! There's a time and a place!
It's important how you respond to Freddies reactions because it's your guidance now which will shape his future.
If Freddie understands what NO means then use it followed quickly by another command like QUIET if he starts barking at someone. Try to distract him from whatever it is he's worried about. Reward him if he stops barking and transfers his attention to you. You may have to work hard at this!

Keep yourself calm. Raising your voice etc.. will make him think what he's doing is right because he will pick up on your agitation. Likewise, petting or cuddling him if you think he has been frightened will also have a negative effect in that he'll again think that he's been doing right. You can even create a nervous dog by doing that.
The screaming child was a difficult one for your hubby as he had a frightened child to deal with and be concerned about as well as Freddie, and it's understandable that he wanted to allay their fears. I'm glad it all worked out.
Good Luck