#kickout

In my headcanon Thunderhoof is from Eukaris and his alt-mode was originally an elk/deer but he needed a proper disguise upon reaching Earth. Being smart, Thunderhoof knew a giant deer obviously wouldn't cut it so he'd search for a more suitable alt-mode, giving up his beast alt-mode in the process and settling for a tractor.

So on the subject of ship children.. Thunderhoof and Knockout's twin sparklings CurbStomp and Kickout were a case of where two different subspecies of Cybertronian, Velocitronian and Eukarian, bred together to create a sort of hybrid. In other words the sparklings are Triple Changers, they can transform into both a Cervid or Automobile. Being a rare chance of protoforming into Triple Changers naturally, they do not suffer the instabilities of those who become Triple Changers through experimentation.