Welcome to the site, Sade.
You'd do well to have a look, and ask your questions, in the Writing For Young Children Group -
http://www.writewords.org.uk/groups/105.asp
but very briefly:
I'd always double space and number the pages (with your name on every sheet).
You don't have to include illustration guides.
Check the website of the agents/publishers you'll be subbing to as they'll have their own guidelines.
Sorry to be brief.
Nik