Imagine...

What if you could change your shape,
Simply by command?
Maybe you'd become a little crab,
Crawling through the hot beach sand.

Maybe you'd prefer to be a lion,
It's almost like a cute little kitty.
Or you could decide to grow wings,
And fly high above the city.

Wouldn't it be cool if you could grow gills,
And explore the deep ocean floor,
Or perhaps you'd be a hungry hungry hippo,
Your only purpose to eat more and more.

If only dreams could come true...
Oh! But they can!
That's the point of imagination-
To bring to life the things that reality bans.

Hi!

You have a lovely idea here. It makes me want to be intrigued by this, if that makes sense, but there's just something stopping me from being pulled in.

I think the main problem is the rhyme - it seems very forced, and it's incredibly restrictive. For example:

Maybe you'd prefer to be a lion,
It's almost like a cute little kitty.
Or you could decide to grow wings,
And fly high above the city.

This doesn't work. It's clearly only put in to rhyme with "city", and it practically bounced out at me as I read the poem. It's not the line you're looking for here.

I won't go through and identify every example of this. It would be tedious for both of us, and would mean you wouldn't be able to improve yourself by looking for these things. But maybe you should try to ditch the rhyme. It takes so much away from the poem, taking the reader out of the story and serving as a constant reminder that none of this is real. You don't want to do that; it's practically a reader-repellant. Your readers should be losing themselves in this poem.

Your last verse, too, should leave more of an impact on the reader. The idea is great, but your presentation could use some work. The line

Oh! But they can!

is broken up by the exclamation marks, and it seems like the narrator is suddenly yelling at the reader in excitement, which detracts from the overall tone.

Well, I hope I helped. Like I said, the idea behind this is nice, and there's a lot you could do to improve it. Please don't hesitate to PM me if there's anything I've said that you don't understand, or if you have any questions.
~Grin

You have a few issues with flow here that I'll address first. They're quoted here:

Maybe you'd become a little crab,

Too many syllables packed into one line.

Crawling through the hot beach sand.

Try to make it simple by just saying "crawling through the sand". Sometimes simple images are more powerful.

Maybe you'd prefer to be a lion,

I would write "Maybe you'd rather be a lion". It flows a lot better.

Or you could decide to grow wings,

Don't know how to fix this one.

And explore the deep ocean floor,

I would say to nix "deep".

Or perhaps you'd be a hungry hungry hippo,

I think only of children's games reading this. Does nothing for me. Get rid of one of the "hungry"s.

Your only purpose to eat more and more.

"only" breaks the flow.

Oh! But they can!

The exclamations points break it visually.

---

Aside from your flow problems, there are a few with the rhyme scheme. You're forcing it in places; it becomes obvious that you only put certain things there to rhyme stuff. BigCheesyGrin said it more eloquently than I can phrase it:

It's clearly only put in to rhyme with "city", and it practically bounced out at me as I read the poem. It's not the line you're looking for here.

^ Same here.

This poem in general is really cutesy, but it's sort of ... meh. By 'meh', I mean utterly forgettable. You could have done a lot more to expand on what imagination is, but you didn't. I'd like to see that.

Good luck.