Keep them curious, answer their questions with demonstrations. Link different parts of the physical world together. Like if one asks where the water goes down the drain, show them the pipes under the sink and show them the pipes in the basement. When you next go on a walk, point out the manholes and sewer grates. Encourage media that will expose them to the nature of things. Mix in some Planet Earth with the other tv. Add "The Log Hotel" or "The Salamander Room" to the bedtime reading. Try to get them to catagorize pine needle trees vs leafy trees. Maybe in a few years draw them some different triangles and point out how the corners look different to introduce the idea of angles. Give a 5 year old a ruler and a protractor and show them they can measure anything they like. If you show this around the time you're buying furniture or moving house they'll likely see you measuring stuff too. They wanna be like you.
Everyone likes to talk about games and curriculums. Obviously kids who do more arithmatic get better at it so playing cribbage can be an advantage at the elementary school level. Playing liars dice can be super enticing for 10 year olds to learn probability (they also learn how to watch people playing games). But ultimately if they grow up and choose their undergrad but dont have a genuine curiosity for "how the world works" it doesnt really matter what specific skills they've acquired.