If your parent is diagnosed with crohn's, should their adult child be examined for signs?

Be aware of signs: Crohn's disease does have a genetic predisposition. Like many diseases, however, the genetics are not straightforward. Different family members may express different aspects of the disease, or none at all. Or other family members may have the same gene but different diseases, such as ulcerative colitis, behcet's disease, diabetes, or thyroid disease. Any signs of disease should be evaluated.

Not right now: Crohn's disease has many genetic components so it is too complicated to say for sure what the risk is that your children will get crohns. However the risk is definitely elevated above the general population--perhaps a 5-10 fold risk above someone else of your same ethnic background. No screening is necessary but if the child has GI complaints they should be checked out.