[kleiba]

There are so many ways you could handle this. But I think the most important thing to remember is that not the system should be the focus of the game but fun. Don't just improvise the plot (according to your player's actions), but improvise "the system" as well -- after all, it's yours, and your only duty is to make it fun for your kids.

Forgot a certain ability on your streamlined ability sheet? Well, who says they all have to be determined beforehand like in DND? Just make them roll new ability specs just when you need them.

Or simply make due with what you've got, e.g. by adjusting what you originally had in mind for the enemy attack with what is possible within your simplified system. And for the next game, slightly update the system whenever you've identified an oversight.

Don't sweat it, the exact rules are not so important, as long as your players can rely on consistency (as a proxy for fairness). For kids, I think, in the end they're gonna love it when they can just roll some dice every now and then and observe how what their characters do results in success when they roll well and (non-catastrophic) failure when they don't. Other than that, I would imagine the theater-of-mind aspect, i.e., the plot and the general world setting will probably be much more important.

[veilrap]

Modern (5e) D&D even explicitly encourages this with it's skill system. DMs are encouraged to just pick a stat (or even let their players pick a stat) that feels like it's applicable to the situation, then then add that to their roll.