one of the things that impacts pacing is extra words. Cut any unnecessary word to have the quickest pace.
Jane tumbled. She landed at Henry's feet.
Jane tumbled head over heels down the mountain. She landed face down, her head against Henry's black loafers.
You can see the change in pace here. Of course, these extra words would be cut for illustrations in most picture books anyway.
Visualize your character climbing a mountain. Each scene should be another step up the mountain or a slide backwards. The climax is at the top. The end of the story is the slip down the other side. Each part of the climb builds on the one before it as if you are building the mountain while they climb it.
I hope this helps.