Ask HN: What's the coolest tech you got this Christmas?
see title
For my nieces and nephews, however, I bought them the large Snap Circuits 750 kit, and we have been playing with that. After they build something, I make changes to it, & they try to predict what will happen. Regardless of their answer, we then test it to see what will happen, & then I help them to understand why. They're getting better at it!! :D