When children address their parents by their first names, it does not generally means that they do not respect them, I think that the children who does this are plain and simple got accustomed to it because the parents find it cute when they are still very young and did not try to correct it and change the way their children are calling them. So, children get the habit of addressing their parents by their first name, but they know that they are their parents. When they become older, I think it 'll change. I based this opinion with a cousin of mine, when their kids were still young 2-3 years old, I'd heard them all the time calling their mom and dad by their first names, but now they are already 7-8 years old, kids call them mom and dad.

Of course, when you and I, will hear kids calling mom and dad their first names, it's kind of shocking and find it disrespectful because it is not natural. We do advice the parents and criticize them especially if the kids are past the toddler age, it is not cute anymore and kids can understand better when they are schooling already.

I think if the parents alright with it and find that their kids does not disrespect them by addressing their first names, then it is up to them. They will just have to be accustomed to people getting shocked and criticizing them for it. Because it is really not nice to hear a kid calling his/her mother or father casually by their first names, yes it is inapropriate, but judging it why or how it came about is hard.