Kickstarter campaigns don't normally get that much love here on PH but this seems to tick all the boxes. It's a buildable bike for kids. Not only does it get kids involved in learning, engineering and the value of play but they get the best reward once they've built it! The kids will also value the bike more (because they built it!) according to the Endowment Effect: https://en.wikipedia.org/wiki/En...
Created by Nikolaj Blinkenberg Willadsen, here's a little more about the product:
"You start out with the the basic bike, which is a high quality balance bike with an integrated tool compartment with tools and assembly knobs.
You can either and purchase the basic bike, a kit or some of the accessories piece by piece, making the Blinkenbike a perfect gift where everybody can contribute - the accessories can be attached in many different combinations and fit together. Some are made for a specific placement and purpose, some can be attached on different places. Only the panniers and the doll seat need another accessory (the Rack) to be placed. As a grown up, you can also be a part of the fun making cardboard accessories for your kids bike. The Blinkenbike will be delivered in a cardboard box with printed motorlayouts ready for cut-out and attach on the bike - creativity is the only limitation... "