Billy Bonkers: Not My Pants! by Giles Andreae

There's something Billy Bonkers doesn't want you to know. Come closer...I'll whisper it: he has to wear his sister's underpants! And whether Billy's flying round a go-kart track, chasing a very smelly dog, or finding some priceless long-lost treasure, it's not easy to explain: "They're NOT MY PANTS!"
Binding: Paperback / softback