I dont think you were irresponsible at all, you did the best you could and were very brave. Horses are horses at the end of the day and even the best behaved ones can freak out, unfortunatly there are people out there who have no respect for others.
Hacking can be dangerous but what can we do.. never go out coz its irrisponsible of us to take a horse (yes an animal with instincts) out of the school?? All we can do is minimise risk, which you did. Taking your 4yr old out for hacks like that is good education and you should be applauded.
As for that woman, if i counted the times i have come across people like that i'd be here all day. My poor horse and i have been attacked by dogs, abused by walkers and dog walkers, nearly run over etc etc. Only the other day my mum had to call the police because a dog walker tried to run over her over on her horse (missed them by a millimeter) with his car, then got out of his car and threatened to set his dogs on her saying 'i f****** hate horses!' I had someone stop their car right next to my horse and lean on their horn for about 30seconds before storming off.
Poor thing, i feel so sorry for you and know how you feel
You are not at all irresponsible. Whether the horses looked at the pushchair or not is irrelevant, as at that stage they had not spooked nor put the walker in any danger. The problem, if I understand your story correctly, were the lose dogs which the owner refused to control even after being asked to do so. If someone asks you to put your dog on a lead because their horse is scared, or they have a phobia or they just think it is dirty and they don't want it anywhere near them, you don't stop to discuss it, you just do it.
p.s. I have four dogs, they are fine with horses (and people and other dogs) but if they are not already on the lead, they are always called back and put on as soon as we see horses.
Glad you are not too badly injured - it could have been so much worse. Loose dogs and dogs that run out at horses annoy me too. (I have 3 dogs). My horses are quite good with dogs as they have been hunting where hounds are often popping out of the undergrowth!