The Baby Rainbow Ponies were released in Year 9 of the My Little Pony line and featured baby ponies with rainbow-colored hair. Adult Rainbow Ponies were first released in Year 2, but despite their popularity, there were never any rainbow baby ponies released before this line.
The ponies in this line include Baby Brightbow, Baby Rainribbon, Baby Starbow, and Baby Sunribbon. They are not the children of any of the Rainbow Ponies that were previously released.