The following is what SCBWI says about formatting a manuscript so that it is ready to submit:

How to Format Your Manuscript

“All manuscripts must be typed on 8½ ” x 11” white paper in black ink.
» Use 12-point Arial or Times New Roman.
» Double-space all manuscripts.
» Pages should be numbered consecutively.
» The default margin settings that appear in a new Microsoft Word document are acceptable.
If you are setting margins manually, use a 1-inch or 1.25-inch margin on each side of the page…. Do not submit electronically (i.e., email) unless the editor or agent specifically requests you do so.” page 8.

How to Prepare the First Page of Your Picture Book Manuscript

The above is what SCBWI says in its “Book” or The Essential Gude to Publishing for Children.