What's at the Top?

What's at the top of the ladder? Is it the string of a kite on a meteorite, that's attached to a whale who's delivering mail, to a moose in suit who's delivering fruit, while a sloth eating soup, parachutes through a hoop, for a group of iguanas in purple pyjama . . . ?

Young readers will keep guessing the answer to this humorous conundrum until the end - but be prepared for a twist!