That is a wonderful video! It makes explicit a lot of concepts I knew but would not have been able to articulate as well as that -- and taught me some new things as well. I can't wait to have grandchildren so I can share this video with my kids!

Only thing I'd add, to make a balance bike', just take a regular bike, take off the pedals (and cranks?) and drop the seat

The trick about spending money on high-quality kids bikes is, buy them used off craigslist. Not only will you pay less than at the store, but after your kid has outgrown the bike in a year or two, their tiny weight will have caused virtually zero wear&tear, and you can resell the bike for exactly what you paid