Since the Amish/Mennonites are pacifists by nature, the threat from them is nonexistent. Your main threat is on the roads from sightseeing drivers not paying attention to the often slow or stopped traffic. Food purchased at the numerous road side bakeries, cheese plants or home made canned items like jellies or preserves should be considered quite safe. If you buy farm eggs, they will likely be very fresh and tasty.
Animals:Keep in mind that this is not a petting zoo type situation. The animals may bite, kick or step on you, or especially your children. Never allow your child to walk up on a horse, buggy, or other farm animal. Animals in pens may be more accessible, but can pass on other diseases. Touching should be avoided.
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Being in the center of Ohio's Amish Country, the world's largest Amish settlement, much of the population is bi-lingual, speaking both English and a dialect of German called "Pennsylvania Dutch." Smaller children speak only this dialect until starting school. The name "Pennsylvania Dutch" is actually a mispronunciation of "Deutsch" or German. Church services are held in "high German," as opposed to the dialect.