Educational and fun
I received the 8 in 1 Solar Educational Kit for free from @playwithunicorn and I loved playing with it. The kit starts by building two modules, and then there is a choice of building 8 different mini robots using one or both of those modules. There are also disassembling instructions, so you can move onto the next robot if you want. Building two main modules and the dino walking robot took 45 minutes total, including figuring out the instructions and fixing a small mistake I made. It's the perfect building kit for a tween or a teen. There's so much physics that can be learned from this kit, especially different types of energy conversion. Learning through play is THE BEST, and I still remember things I learned through hands on experiences like this. I will save it for my daughter to build together when she's older and shows interest, but I can't recommend it more.