From Wikipedia: An early Filmation proposal for [the animated Star Trek] series had children assigned to each of the senior officers as cadets, including a young Vulcan for Mr. Spock. According to interviews with Norm Prescott, Paramount offered Roddenberry a substantial sum of money to abandon creative control of the project and let Filmation proceed with their "kiddy space cadet" idea. Roddenberry refused. Filmation would later develop the idea into its own original live action program, Space Academy, in 1977.
There's been some of the production art floating around with that particular ship design along with the original crew and their younger counterparts for some time now.
Here's the one with the kiddies: http://farm6.static.flickr.com/5161/...e391d5fb13.jpg