Noted: Chariot child trailers ,
http://www.chariotcarriers.com/, share the hitch type with Carry Freedom trailers , their basic Y trailer has a plywood load platform.
Its a Ball and socket affair lollypop of elastomer and the pin closes the front of the socket .
I got a Carry Freedom City trailer , but its a Bag carrying trailer not a Kid trailer , I got it ... trailer not kid,
because it folds within it perimeter frame to be flat .
I tow it with my Brompton ..