Agree with the above.
First off, I know the US market is different to the Australian publishing industry.
However I've worked on children's books before (layout etc) and two things I suggest you consider are the age group you are writing for - is it a picture book for younger children (the ratio of how many words on the page vs illustration), or for young adults.
Also, the choice of illustrator is really important. Someone sympathic to your story and creative. These are things you can discuss with your publisher but are good to have a think about beforehand.
You need to find a publisher who specialises in children's books, also approach educational publishers who know the market inside out.
Acquisitions Editors receive gazillions of manuscripts so send out your concept to as many as possible. But they are your champion who will fight for your story and help realise it. And don't get discouraged because it does take time.
DO write because you
enjoy it and that will resonate in your 'work', but remember that writers rarely get paid very much $. Quality doesn't always equate with quantity of $. So keep your day job, but write as often as you can. It will make you feel rich in the meantime.

Best possible luck and keep with your dream!!!

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