It's hard to tell, shellyesq. Mostly because of the missing 1890 census, it's impossible to know exactly when they were adopted and how old they were at the time. And, although in a number of cases I have figured out who the kids' biological parents were, others are total mysteries. Five of them are just names with no other information at all; I don't even know if their names were given at birth or were given by the adoptive parents. Did they come from institutions or were they hardship cases in the local community? I have no idea.
It's possible that some of the girls were taken on as household help but I tend to think that loneliness was a bigger factor. I do think that the four boys were taken in, at least partly, to serve as farm hands because all of them went to farmers with a shortage of sons. As for the girls, in one case, two young nieces were adopted almost certainly to help out a struggling family with too many children and an almost criminally irresponsible father. In four other cases, the girls seem to have been very young [<2 years old] when adopted. As for the rest, I'm not sure.
It's interesting, too, that this spate of adoptions mostly stopped in about 1910ish. I'm guessing that this happened because adoption became more bureaucratic and regulated and also because people moved off the farms and it was harder to feed an extra mouth.