It's not unusual for a first-time author to have difficulty finding an
agent. When I look at my client list, I see that most of them were
published before they came to me. That doesn't mean I accepted them
because they were already published (and in all cases, these were
publications by smaller, regional publishers), but because they had
perfected their craft before I took them on. They had been writing or
illustrating for years.

So, if you have just written your first book, you might not be able
to find an agent, but that won't be because agents have policies about
not accepting unpublished writers. It will be because you just need more
time to educate yourself about the publishing business and to perfect
your craft. The competition is intense in children's books and often you
are competing with authors and illustrators who have years of
experience.

If you can't get an agent interested in your work, my advice is to
continue to write, go to classes, join a writers' group and get
feedback, send your work out to smaller, independent presses, and keep
submitting to agents, because if you stick with it, you will eventually
get the agent you want.