It's called "White Horses" and was sung by Jacky Lee for a children's television programme of the same name from the sixties / seventies. I remember it was either a German or Austrian production, but was dubbed (badly !!) into English.
Jacky Lee also sang the theme tune to another 70's kids' TV prog - Rupert the Bear - the string puppet version featuring an extremely psychotic Raggety. All together now...
"Rupert, Rupert the Bear,
Everyone come and joiiiiiiiiiiiiiiiiiiiiiiiiii..oin.,
In all of his games."