A few years ago I started an online writing course for children’s books and its a perfect way to learn the craft, what to look out for, how to sell yourself and, with a bonus of a final examination (I got 97%).
It’s a costly course; I think it’s in the hundreds, BUT if you look at Groupon, there typically is a hefty discount available, I’d try that route first.
If you’re thinking of becoming a children’s writer but need a place to start, I suggest here. If you’d like the course book and a certificate, for a small cost you can also purchase them. The Groupon link is here.
The resources and learning material are still available long after you’ve completed each module, so if you feel like having a break and then decide to return to it, all the information will still be available.