This one of seven photos, probably from sometime during the 1910's, that I bought from a local antique shop. They're all printed on relatively thin paper, most of which with a hole punch in the corner.
The girl is identified on another photo as Bessie, but there's no id on any of them for the little boy.It looks like they're on a rather rudimentary teeter-totter positioned just right so that it won't tip them over backwards (likely with the help of the photographer's foot on the other side). I'm not sure what it means, but somebody wrote "Bow" on the back in pencil. It's the same handwriting that Bessie's name is written in.
I think Bessie and the little boy might be cousins. I don't think that they're siblings, mostly because there were other photos of her with another girl who looks enough like her to very likely be her sister and the little boy isn't in them. However, there were enough other pictures of the boy among the pictures that I think they must have both belonged to the same family.