Maybe the first "How come?" question is "How come these books do so well?" And the answer is in how they satiate every boy and girl's insatiable curiosity about the world around them.

Crack science writer Kathy Wollard answers those sneakily simple questions that ambush even the most erudite moms and dads. Like: "Why do apples turn brown when cut?" Or "Why do we get dizzy from spinning around on the playground?" Or "How can a fly walk up the kitchen wall?"

The 125 questions are all derived from the experiences central to a kid's world—stuff that happens at home, in the backyard, at school, on vacation. There are the inevitable insect questions—"Why do bees die after they sting someone?" (the honeybee's stinger is barbed, and can't detach from the bee without pulling out its venom sac, a fatal injury). Food questions—"Is a tomato a fruit or a vegetable?" (a fruit, in fact a berry). Science questions—"We used dry ice in our school play to make fog. How does it do that?" (Unlike water, carbon dioxide goes straight from gas to solid and back—when frozen as dry ice, it "melts" into fog.) And the classic: "Why can't we tickle ourselves?" (Tickling depends on the ele...