It depends, does your game development tool allow users to create games that they can then download and publish or sell elsewhere? Or will the games they create only be used within your tool ?
Because if using your tool users create a game with my assets and then they publish the game or sell it, it's not good. But if users create their game and use it only inside your program without publishing it or downloading it or selling it. Then it's good because the assets are only used in your program and are not redistributed