Sadly, we don't know that deaf children have access to ASL. Most don't. Theoretically speaking, the potential is there: most deaf children COULD have access to ASL, but in reality, they don't.
ASL is wonderful -- if you've got it. But for the average deaf child born into a hearing family without ties to Deaf culture, it's not there. It's not available in their homes, it's not available in their communities, it's not available on TV, it's not available in their schools, in stores, in libraries, in bookstores, in the museums, on playgrounds, in airports, at the gym, and so on. Their parents don't know it, their siblings don't know it, grandparents and cousins don't know it, their neighbors don't know it, their teachers, doctors, dentists, etc. don't know ASL.
It's not all around them, the way spoken language is, blasting from radios, wafting from doorways, broadcast to the classroom, flowing all over the dinner table, bouncing across the playground. For the average deaf child from hearing parents, ASL is an hour once a week in a special playgroup of children of various ages they don't see again until the next Monday. It's that very expensive and lovely Signing Time collection from grandma that they LOVE, but doesn't provide grammar or more than a handful of vocabulary. It's a parent who thinks he or she is covering a 3YOs language needs with those 20, maybe 50 signs, instead of 1000 words the child should know at that age.
And you'll blame parents for not finding ways to change all of that. Parents finding ways to make over the language of a home, a family, a community, a town, a school, the environments the child will encounter. But ASL is really not all that accessible to parents either. I've cobbled together a means towards learning ASL for myself, with difficulty, but I'd like to find more options, and I know many other parents who are interested, but don't see how it would be possible. I've asked those who did not grow up with ASL how they learned as adults, for tips, programs. Many who advocate so strongly for ASL and against CIs are not even fluent in ASL themselves. Why is that? Because it's not all that accessible.
I've asked those who did learn ASL as children how their parents integrated it into their lives, their family's means of communicating. Most say, they didn't. One or two say, like PFH, through SEE, and ASL was learned on their own. Faire Jour took enough courses over a year or two to qualify at an interpreter level, joined a deaf church, immersed her family in deaf culture. I'd like to know how wee beastie does it, how Jillio did it, how Rockdrummer does it, how other hearing parents with children using ASL were able to make it happen. But I don't think it's easy, and it's certainly not accessible to a child without extraordinary intervention by parents.