Sorry for the OT but I don't know where to ask this, really - I searched the web but no joy. If anybody knows a good resource to search or a place I can post without additional registration, that'd be great. Being able to ID this would be even greater.
I suspect this was a juvenile from the 70s or so (conceivably 60s or 80s). It featured children riding on the shoulders of other children (or conceivably just running around) pretending to be knights with lances riding horses. It seems like they wore wooden "sandwich board"-like things over their torsos like armor. It also seems like they played really rough but in good fun but something happened - SPOILERS ahead - where two of them began fighting in earnest and the lance or chest armor splintered such that one of the boys was killed. It wouldn't surprise me if "horse" or "battle horse" or something was in the title, but it could just as easily not be. And I seem to recall the cover art (hardcover dustjacket) being predominantly white, with maybe a sort of "progression of line-into-color" sort of art that may have depicted one of the horse kids or something.