Hi Erin,
In my experience it's rare for a publisher to say they want to see page breaks. Given that, you may not receive lots of advice here. Given that too, here's a short part of my published nonfiction picture book, I've Got Feet!, which shows how page breaks were indicated. However, this was towards the end of the editing/revising period with my editor so someone else may well chime in with other recommendations.
Best of luck with your sub!
[pg 1]
design/art
[pg 2]
copyright info and dedication page
[pg3]
Title page
[pg 4-5]
Animal feet can walk, run, and kick. They can climb, jump, and dig. Some feet swim. Some catch food. What a lot of things animal feet can do!
[pg 6-7]
I’ve got fast feet! My feet are as quick as a car on the highway. Sidebar: Cheetah feet never slip. They have claws that grip the ground (even better than soccer shoes.)
PS Note how the double page spreads are indicated.