I would spend a good two hours on google looking up children's book related communities and putting them in an excel spreadsheet. You can then create an engagement strategy out of those resources. This is what I usually do when researching for articles or when creating media lists for CrowdfundingPR.
Once you do that research, be sure to share the findings with us (or I can publish it as a blog post and credit you) so that other creators can benefit.
Also be sure to check out this interview with a children's book creator:
http://www.crowdfundingpr.org/janky-pat ... ckstarter/