I've been working on an open license for Hero Kids compatible products and a compatibility logo to go along with the license. The license is based on the O.L.D./N.E.W. license by Russ Morrissey.
Here's the current draft of the license. Any problems?
Acceptance of Terms
By displaying the Hero Kids Compatibility Logo on your product or associated materials, you accept and agree to be bound by the terms and conditions of this license agreement.
Royalty Free License
Third-party publishers are free to create and sell content for Hero Kids. You can create sourcebooks, adventures, resources, expansions, and use the Hero Kids Compatibility Logo to indicate compatibility with Hero Kids. You can also make or sell electronic applications. The license is free, and you do not need to ask permission or submit an application to use it. If you make a product that is compatible with Hero Kids, in addition to ensuring you do not infringe any intellectual property, you must acknowledge the Hero Kids trademark, only use the Hero Kids Compatibility Logo, and ensure your product does not copy the Hero Kids trade dress or include any Hero Kids trademarks in your product's title.
Hero Kids Trademark
If you produce a product, web page, or app compatible with Hero Kids, you should include the following text somewhere visible - at the bottom of your web page or on the credits page of your book (in at least the same font size as your own copyright notice):
Hero Kids is a trademark of Justin Halliday and is used with permission. No challenge is intended.
Hero Kids Compatibility Logo
You can't use the Hero Kids logo on your product. However, you can use the Hero Kids Compatibility Logo. The logo must be smaller than the title of your own product.
Ensure your product's trade dress is visually distinct from official Hero Kids products produced by Hero Forge Games (Justin Halliday). Additionally, don't include any Hero Kids trademarks in your product title.