Tyvek is a great idea (some commercial children's books use this), but if you want the "board book" feel, then printing on paper that is glossy only on one side

Tyvek is a great idea (some commercial children's books use this), but if you want the "board book" feel, then printing on paper that is glossy only on one side, then gluing to cardboard will work. Just make sure to print the page image slightly larger than the cardboard so you get full-bleed after trimming.