While toys are always fun, in case of STEM I would focus on developing active attention. That is not just immerse but also observe the result (success or failur

While toys are always fun, in case of STEM I would focus on developing active attention. That is not just immerse but also observe the result (success or failure), think of ways to make it better. Basically developing the cause-effect pathways, letting kid identify and solve a problem. Tons of chances for this with everyday objects. Once kid is able to scribble, make him take "notes" of observations. Say, kid plays doctor and receives teddy bear as patient, asking what bothers him and taking notes of that. Measuring temperature with beeping thermometer, then deciding if there's fever and "prescribing" teddy bear some remedy or regimen. Look around your house, there lots of safe objects that can be used as functional "toys". After all kids want to adapt to the "grownup" world.