If you wanted to clear a room full of nervous mothers of small children you could to it by yelling one word: “Chemicals!” Jessica Alba — famous for her roles in “Fantastic Four” and “Little Fockers” — knows this, and has built a booming business around modern, hand-wringing parents who worry about the prevalence of chemicals in everything, from toys to food. The company she co-founded, called The Honest Co., launched in 2012 selling personal care and home products for little ones like diapers, bath products, laundry detergent and more — all made with nontoxic ingredients. The company now touts...