Archie's growls are an indication he is not comfortable.
I am in a similar position, so I will try and explain out situation and how we manage it.
Honey is 5.5yrs. She is a very anxious dog, but responds very well to positive training. She is prone to guarding things - primarily from other dogs, but with highly treasured items she does show low-level guarding tendencies to humans (reluctance to retrieve, snatching items etc). She is also not confident around children - we didn't know any children when she was a pup, and her early experiences were not entirely positive.
I have 2 children - currently 2.5yrs and 1yr old, so what follows holds true much more consistently for the older one than the younger one, but the younger one will get there in time.
Both children know that they need to give Honey space. Honey will growl if she feels threatened by their presence - we then step in to direct the children away, but we also work at teaching Honey how to move out of the situation. We have a very strict "let sleeping dogs lie" rule - Honey can approach the children and then the children (with our help) can pet Honey (or give her a treat), but the children know not to approach Honey. We spend a lot of time helping the children to give Honey treats (or kick her ball for her), so that she views them as something positive.
If there seem to be times that Archie is more "grumpy" than other times, have you checked out a physical issue? Honey has a bad back - she has a tight muscle that can flare up causing twitches (and pain) and she is certainly less tolerant when this is causing her any trouble. We saw a McTimoney Chiropractor who highlighted the problem and showed me how to ease it. This makes a huge difference.
