Brain builders & Squigz kit

Mechanical engineering and simple machines / Robert Snedden

Garfield's Almost-as-great-as-naps guide to engineering / Rebecca E. Hirsch

KEVA brain builders STEM kit (20 precision-engineered pine KEVA planks, 20 double-sided puzzle cards, 1 zippered carrying case)

Squigz (assorted pieces with suction cups).