Sounds like fun! Last time that DS5 helped me bake he was doing a riff on the cookie sheet multiplication and division that Debbie mentioned. Baking has lots of opportunities for experimentation and math learning, and chemistry - isn't there a Kitchen Table Math book somewhere? Plus, then there is eating the results.

Pendulums, that could be fun too - I'm thinking of swings. You could make a playground for Playmobil people (or something) and then do experiments with different lengths of swing ropes. Try changing the mass of the object too, how swing is started. Take notes...

I think, stuff does get committed to memory, but there is more than one way to do that. If you're doing experiments, or playing, then you might be more engaged and likely to remember the result.