Illustrations

Good morning! Hope everyone's day is going great so far! I have a question, like that's anything new...

My oldest son is a natural artist and I want him to sketch some illustrations for my current novel to be used on different pages.
 Let's say your chapter title page is about phone calls or ice creams, or puppy dogs, I don't know whatever comes to mind.
 Anyway on that page I'd like to have a sketch along with the chapter name.

 I've seen it done on other books, but what I want to know is when you send your novel off to the agent or publisher should you have the illustrations on the pages that you want when sending it in.

 Or should that be something discussed when you are working on the details of the cover and publishing it?