I would go with the first design, this is a kids book and the classic jet style serves 2 purposes:

1. It can land and introduce shartzy without looking too out of the ordinary (as if a UFO landed).

2. This playful looking "jet" can fly to other planets is a concept that is best left for introduction AFTER the reader has familiarized themsselves with the jet

Right now shrazi has been adding elements that match texturally within his overall visual concept

And the twist in the story with steemjet landing and introducing SMT is going to go waaaay over the heads of most, therefore, it is best to delay the introduction of the most confusing and difficult to comprehend concepts as late in the story as possible, so at this point in the story, I suggest we land a rather "normal" looking "jet" on the ground so as not to let the reader know that he is about to take a trip to the moon, this will make the trip to outer space all the more impactful, because we won't lose the reader until the moment we launch. We don't want to lose the reader when a UFO lands here now