This was lots of fun, but still needs tweaking, in my opinion.  It works well on the teeny chairs at the nursery and on dining room chairs, but really needs a longer waist strap for restaurant high chairs.  I’m still debating how useful it is for us, but it is definitely cute.  The tutorial can be found here.

It works in similar fashion to a diaper, really.  For squirmy little ones, like Benjamin, I’d recommend lots of sewn on velcro!