Hey, thank you for playing and taking the time to write down here.
As far as I know, no there isn't a walk through available yet showing up to level 18.
Indeed, you don't need the double jump ability. Baby Dino doesn't have such ability even later in the game. If you feel like tops of palm trees aren't clear enough to identify the platform area, then I will have a look and see what I can do there. I'm pretty sure I can adapt the assets and find a way to make it visually easier to understand such thing. Sorry about that.
You won't be able to find any keys as there isn't any at the moment in the game. I'm still developing it, and the key feature is still on the works. I plan to add some sort of merchant levels on the map where you can go, meet a dino merchant and buy those keys to unlock extra not story-related secret levels. It's in progress, and will come together in an upcoming update.