In Massachusetts, children cannot be denied private health insurance because of a pre-existing condition. I can’t believe that Maryland is much different.
I don't live in MD, but to my knowledge, MA is unique in the country with the way it handles health insurance (Gov. Romney's health care reform law.) From what I understand, pretty much every other state hasn't changed - private/individual policies can be restricted to those who have no significant illnesses or pre-existing conditions.