Found the patent for the swivel, and it is effectively from 1877: US Patent 190,421 by Andrew J. Davis of Pittsburg. Here is the drawing:
In the description of its use, the patent uses the generic term "child", not boy or girl.
The patent only has one claim and it is for the swivel, but interestingly it also mentions the weight ring which is prominent in the drawing: "The top C, represented in the accompanying drawings, is furnished with a metal ring, secured to the body of it, for the purpose of giving it greater force and a more steady action in spinning."