I wasn't going to post on this as everyone else has it pretty much covered, but then I changed my mind. I currently have a very large, very strong very hormonal ram running with my girls, and should this have happened in 'his' field with 'his' girls, he'd have butted them. He could easily knock an adult man off their feet, so I could imagine what he'd do to a 2 year old.
My yard is full of signage, like everyone else's would be too - only authorised personnel, livestock can be dangerous, don't touch the machinery - all the signs that farmers have to have up now to meet various health and safety regulations. And yet, when livestock turn on members of the public who have no business being on the property in the first place, who are they going to try to blame?
So, op, if your ds's experience had gone differently, if the ewes had aborted, would you pay the market price for the lambs? If the ewe had died from the stress of being chased around her own field by strangers, would you have paid the market price for her? Or if there had been a ram who took umbrage to your presence, who would you be blaming and shouting at about keeping 'dangerous' animals?