We have an older retriever mix that sounds like yours--just about perfect. He had been an only dog for years though, and so we thought we wouldn't get another one until he passed.
That didn't happen--we got a 7mo dog from the shelter a year ago out of the blue when I found a photo of the pup and had to save him. Older dog was excited at first, and then about a day later was like, "Okay, you can take him back now..." There was some assertion of dominance for a while--nothing major, just growling--and now, our dogs are pretty tolerant of each other. Older dog doesn't get too bothered by younger dog, and younger dog would be lost without older dog.
As far as teaching the young dog--our young dog definitely picked up some behaviors by example, both good (being chill) and bad (jumping on furniture). I wouldn't say old dog "taught" him anything, but he definitely was an example that our younger one has followed.
With you having kids, I would do this very cautiously, mainly because of the dominance thing. I would hate for a child to get involved in that.