Thanks for the suggestions, those are good ideas. The Hiscocks are not in my family tree. I found them living with my ancestors, the Comstocks, as "bound" children, and just decided to look into it. I don't know how they got to Minnesota, perhaps they did travel with their mother or another relative. I also don't know how they ended up as bound boys and girls, the orphan train is just a guess.
By 1930, Frank Hiscock was living with the McMurtrie family, and he is listed as "brother". So, at least some other family members made it to Minnesota.
Hope this helps anyone who may be looking for info on those children.