Not sure about THE best, but here are some ideas:
On the chance that you mean children's writing as that actually written BY children, here are some ideas for that, too:
A writing contest could be the Young Author.
An Essay Contest is properly defined as a written kind of contest. Writers can truly show off their skilled writing talents in these kinds of contests, it is like a spelling bee, but you are writing instead of just spelling, and the essays would be graded in the end to find out which is the best.
LuLu.com, this used to be poetry.com. This site is not just for poets or poetry, there are contest for short fiction, prose, childrens stories and science fiction.
Win a photo or writing contest.
Cardinal Glennon Childrens Hospital!!!!!
One way to get discovered is youtube or facebook, or enter a writing contest and submit writing, or enter an art contest and submit some art.
Ewen
(1 pt) Angela used a time machine to win a writing contest.
Times New Roman
Yes she must love writing books, she has wrote loads of fantastic childrens books.
Writing Elder Childrens Literature Such As The Book "Holes"
Justin Bieber