I was diagnosed in late 20s. I have 2 kids, ages 9 and 6 neither have UC. I was the first in my family history to have UC. So from my perspective hereditary doesnt play that much of a role. I do have a family history of the following mental illness, heart disease, breast cancer, thyroid cancer, bladder cancer, rhymtiod arthritis, and I'm sure I'm forgetting a few at the moment. Did any of those stop me from having kids - no. So why would I not have kids because of worry of passing on UC.
My 9 year old does have asthma and no family history of that whatsoever. So really what diseases children may or may not end up with is not entirely made up by family health history.