This is cute! I like the idea of showing that progression of growth and the animated preview works really well too. I think the clouds could use a little more definition, since in comparison with the wonderfully detailed earth they seem sort of simple, but then again I'm no expert : P Good luck with the challenge!
I think the mower could benefit from a shadow underneath it, as of now it looks like it's further back from the foreground. Perhaps you could make the grass infront of the mower more long and untrimmed looking, just a suggestion.
Thank you :)