Lets begin with a gadget that kids will love and learn from. A projector for their smartphone. These little boxes have a lens that allows the screen to be projected onto a bedroom wall. The quality is good enough to give kids the feeling that they are watching a movie but since these toys are mechanical rather than electrical, the kids may even learn a thing or two about the physics of light, A great reason to buy them one of these. Besides, when they want to watch Frozen for the umpteen millionth time, you could send them to their room and let them watch the trailer on youtube instead.
While we are on projections, what about a home planetarium. Project the whole universe onto the ceiling. Not only is it educational, but its decorative too. I like the details on this one and the setup is easy.
Rubber Band Racers are a good way for the kids to enjoy some healthy competition and build cool toys too.
Microwaveable Bagpuss is the best alternative to a hot water bottle ever invented. And when Bagpuss goes to sleep all his friends go to sleep.