For the over-stretched parent who doesn’t have time to puree plums or soak grains overnight, portable plastic packs jammed with organic and healthful ingredients are a godsend. On-the-go moms can just twist off the cap and hand a pouch of blueberry flax and oat to a hungry baby to suck on by himself. No spoon or spoon skills required. While these packs are pricey ― a 4-ounce pouch can cost north of $2  ― families are willing to fork over the funds for the convenience factor. But this convenience comes with another price: Most of these plastic pouches can’t be recycled and are destined for landfills ― or worse, the oceans. The demand is growing even though reasonably priced alternatives are available that can be used over and over again. The problem...