Happy Mother's Day to our mom, who we used to think was so strict. She insisted we make our Halloween costumes and the gifts we gave at Christmas and for birthdays. We had to make our beds every day and write thank-you letters for every gift we received. We even had to write letters home from college. Every Single Week. But all those letters taught us how to put our ideas into words and images on paper. We thought we were writing for her, but it turns out it was really our mom's gift to us. She and our dad taught us everything we know, so of course, we dedicated our first book to them. But the truth is, every book we make is a thank-you letter to our parents. A thank-you letter and a love letter, too.