Only just spotted this, or I would have replied sooner. I realise, as Doganjo pointed out, that any youngsters would be dead now, but for future reference, my thoughts might be of use.
I did once find a leveret on a farm where I was working. It was more than 50 years ago, so I can't remember the details, or what happened to the mother. However, I did raise it and let it out again. At that time I would probably have given it baby formula milk, but now I would source goats milk, or look on the internet for something more suitable.
As what to do on finding a dead female - I would first have a good look and see if she were lactating. If absolutely no udder development I'd assume there were no youngsters. If she seemed to be producing milk, I would have a good search in the area with my dog on a lead, or even off the lead if the dog weren't a killer - for a really efficient search.
Hopefully though it was a once off.
I don't think it's fair though to necessarily blame the drivers. Animals/birds run out so quickly, and even at a steady 30mph it is often impossible to miss them. I imagine very few people would want to purposefully hit an animal - if only out of concern for the potential damage to their car.