Charles Ingalls never filed on a homestead claim in Kansas because the land wasn't yet open to settlers; it was still Osage land. However, Charles and the other settlers mentioned in the book had heard that the land would soon be open, and they knew it would go fast. The best way to be sure of getting a good piece of land was to get there before it was open for settling, and that way as soon as it was available, they could file their claim--first come, first served, so to speak.
Comment: And people wonder why the Indians fought back against white settlers? Even "innocent families" like the Wilders were illegally trespassing on Indian land.
White folks have rarely hesitated to evict squatters and trespassers. Why shouldn't Indians have had the same freedom to protect their property?
For more on the subject, see Little House on the Osage Prairie and Little House on the Prairie.