If you want to donate to a legitimate, well respected charity that benefits Lakota children, I'd suggest One Spirit
https://www.onespiritlakota.org/ They do very good work. I have been donating to them for years. They do not over-solicit, and the funds go directly to help the people.
St. Joseph's Indian School is a legitimate school, but it does have a bad reputation regarding it's fundraising practices. Those problems may be in the past, but I am not sure enough about it to donate to them myself.