I've worked with a lot of first-time picture book writers, and almost every stuck project has the same root cause: the idea is a situation, not a want.

"A dinosaur who lives in a city" is a situation. It's not a story yet. Kids' books work because a character wants something specific and runs into trouble getting it.

Quick fix that works almost every time: take your idea and finish this sentence — "[Character] wants _ but _."

Example: "A dinosaur living in a city wants to make a friend, but everyone's too scared of him."

Suddenly you have page 1 (the want), a middle (the trouble), and an ending (how he gets it, or realizes he wanted something else). That's a 32-page picture book structure in one sentence.

If you're sitting on a picture book idea that feels "stuck," try running it through that formula in the comments — happy to help you find the want/trouble in it.