The jaw changes size and shape quite a bit before the permanent teeth come in. Weston Price showed photos of twins, one breast fed, the other bottle fed. The breast-fed one had more prominent cheekbones and wider palate just from how the harder suckling required to breastfeed causes the muscles to pull on the bones more. The wider palette allows for more space in the horseshoe of teeth, so the teeth aren't crowded. If sucking can change the shape of your jaw, chewing can too. Also, babies not fed grainy pablum would start chewing earlier.