aaw Jen - poor you. You want walkies to be nice times don't you, and when they're like this you just don't enjoy them
I think it probably is a "being on the lead" thing, also prob to do with his age, thinks he's a big tough man - you know the thing ;)but he's got to learn that this behaviour will not do.
I think you need to spend some one to one training, without children. Keeping him on the lead, approach other people, children and dogs and walk briskly and brightly past, chivvying him along, use liver cake, I recall Monty likes it
, to bring his attention to you. Make him always walk to heel on the lead. Give him gentle praise when he's walked past nicely and firm no's and more chivvying when he's looking dodgy. Try not to do the natural thing, ie reassurnace, sshing etc as that reinforces that he has something to worry about. If you are bright and confident and show him you are in control, then he'll be more comfortable.
Then try introducing children and the buggy. I'd start with an empty buggy so that you don't have to think about the unthinkable happening. If an empty buggy goes over, no harm done.
I used to have this with Jasper and I used to get upset as I felt so embarrassed. I did all the above, only without the buggy - past that stage
, and before I'd even realised it, he'd stopped taking any notice of passers by. He will occassionally make to bark and mess about, but a sharp pull on the half check and a firm no, gets him back to me
Good luck and give him a "don't be a naughty boy" hug from me and the boys send "good lad" "keep it up" licks :- sorry :-