"And it shall be when your son asks you" (Exodus 13:14): from his asking and from his speech you come to know what is on his mind. "And you shall say to him": that you should not be ashamed to tell him. Rather, the very matter of which you are ashamed, anticipate it and say it [first].
Answer Your Child's Question Without Shame
Mekhilta DeRabbi Shimon Ben Yochai 13:13
והיה כי ישאלך בנך משאלתו ומדבורו אתה יודיע מה דעתו: ואמרת אליו. שלא תתבייש מלומר לו אלא מלתא דאת בהית מנה הקדם אומרה: