Hey, thanks a lot for your interest and for your question!
In games inspired by Into the Odd, special abilities such as magic are typically achieved by magic items/special equipment. They typically just work but have some limitation (e.g., need recharging in specific ways). So by default, I would say just let them do it, and embed the consequence/limitation in the item.
That said:
- Depending on the age and character of the kids, you may want to be even more forgiving, and also not care about balance that much. (I might give a more powerful item to a 5yo that I wouldn’t give to a 10yo if they play together.) You might even give Oddlings innate special abilities.
- The examples you gave are on point. If the situation creates danger from using magic, the ability to roll against is dictated by the situation. If you wanted to include some inherent risk/backlash from any use of magic, I would probably use Smile as the default roll (using magic strains your confidence and good mood).
Again, thanks a lot for checking out my game, and may you and the kids have a great time together. :)