In the original manuscript, Oliver Cowdery initially wrote “they have bore children”, which he immediately corrected by overwriting the final e of bore with an n (there is no change in the level of ink flow). The original text has numerous examples where the past participle is identical to the simple past-tense form (as in 1 Nephi 5:1, “we had came down” rather than “we had come down”). Thus one could interpret the initial bore here in 1 Nephi 17:20 as a past participial extension of the simple past-tense form bore (as in “they bore children”), although usage elsewhere in the text suggests we should actually expect “they have bare children”, from “they bare children” (see the discussion under 1 Nephi 11:7). For a complete listing of past participial forms based on simple past-tense forms, see past participle in volume 3.
Here in 1 Nephi 17:20, Oliver Cowdery’s corrected born undoubtedly represents the reading of the original text (although in standard English the spelling is, of course, borne). There are seven other passages in the text that have the past participle of the verb bear, and in each instance the form is borne rather than bare or bore. (The standard spelling borne is spelled variously in the manuscripts as bourn, bourne, born, and the correct borne.)
Summary: Follow Oliver Cowdery’s immediate correction in 1 Nephi 17:20 but with its standard spelling borne (“they have borne children”); the use of the past participle borne agrees with all other usage in the text.