Aquila magazine out of the UK is a pretty interesting market for children’s fiction and non-fiction. I get the feeling it’s pretty hard to get in to, but there aren’t a lot of venues for work aimed at that audience:
AQUILA has a dedicated team of regular contributors who are experts in various subject areas. Many are teachers in their field, and so they’re used to communicating with children. Occasionally unsolicited articles are published if they are highly original and engaging, and based on specialized knowledge. Articles and stories are planned up to a year in advance. A selection of fiction is made each summer, the themes for the coming year are posted on the website in September, and most non-fiction is commissioned by the end of November for the following year.
They pay 90 GBP for fiction and non-fiction (note: You do need to query for non-fiction). Fiction should be around 1,000 words and features around 800.
Literarium listing is here: https://literarium.net/market/new-leaf-publishing/aquila