I was a child of the 1970's, so here are some of my earliest gadgets

The Little Professor is a backwards calculator designed for children ages 5 to 9. Instead of providing the answer to a mathematical expression entered by the user, it generates unsolved expressions and prompts the user for the answer

Merlin (sometimes known as Merlin, the Electronic Wizard) was a handheld electronic game first made by Parker Brothers in 1978. Merlin is notable as one of the earliest and most popular handheld games, selling over 5 million units during its initial run, as well as one of the most long-lived, remaining popular throughout the 1980s.