We adopted a child whose bio mom was Hep C positive. We didn't know that our Ds was not HepC+ until his third negative blood test at age 18 months. We didn't know he was HepC possible until we brought him home (at 14 months old) and our PEDIATRICIAN caught it in the medical records at the first dr visit. So we had to play catch up and figure out what we needed to do. (Um, don't know what the cw was thinking? Or why it wasn't in the info we were given? But anyway....)
We just took 'universal precautions' and were careful about blood contact. (He often had bloody diaper rashes that went with his food sensitivities/reflux stuff.) He ended up being negative, happily!!, so we didn't have to do much beyond being careful during the time we were waiting to do the final test.
And yes, a child who is HepC+ is 'contagious', maybe not by coughing and that kind of thing, but by blood to blood contact so precautions should be in place.
We fostered my niece and weren't told about the possibility either only because my sister told me, I knew and the birth report. It's crazy you can adopt a dog and by law they have to tell you the dog has heart worms, but take a child into your home with a very serious blood transmitted virus, and they aren't obligated to tell you, and I have other young children I have adopted. Her doctor hasn't actually tested her yet just her white blood cells are low, her platelet count is high, she sleeps a lot and gets tired after playing outside, like every kid does, but I feel it's a bit quicker than the other kids, but she just turned 2. She also most likely has autism like her 2 brothers and she isn't talking yet. But she is trying and she is smart and loving and still communicates in her own way. I started teaching her sign language when we got her at 3 weeks after going through her brother not being able to talk until he was 3. Back to my point it just amazes me the CM didn't tell us either yet the pound was legally obligated to tell us about heart worms in an animal and this is a human being.