Played with my Son (8) who found out a gamechanger-tip: 

pressing SHIFT while driving speeds the vehicle up

Some more tips:

It really helps to just keep trying (and re-reading the instructions).

You need to use the arrow keys to switch from trees to grass -- so if it seems to refuse to plant, that'd be the reason why.

There seems to be more dirt available than is needed for the plants.

You don't have to fill the container in one go (but it will only launch when 100% full).

Press C twice to zoom out. While waiting for the pod to land, I drive across the planet (with the Shift key held down of course).  

Thanks for making this, it's great.

I loved the concept, the music, the growing plants.

I wish there was a Pause option, and a way to tell "how much of the last day" remains, because you just have to guess otherwise.

Also, the instructions hint that you could collect seeds ("seeds you receive or collect") but I couldn't find any, not even in the crops I already had growing.

In any case, great job!

Hey, thanks for the feedback! This was a fun little game jam project to be a part of. Your feedback is right on the nose, haha. I'm glad you guys were able to figure out some of the more obscure (we ran out of time for a proper tutorial and I definitely could have given the instructions another look over, the seeds concept was a dropped idea near the end) commands, that makes me feel pretty good about what I helped make.

I'm glad you and your son made it through and had a fun time figuring it all out!