Bhookad Zinga is not a title many recognise, although the cover of this children's book - run over by a monstrous stubbled caterpillar in graded colour - is eminently familiar to urban English readers. Only, they know it as The Very Hungry Caterpillar. A book by another name is not always another book. Not on the bilingual shelves.   If you look twice today at the children's corner of bookstores, you won't be faulted for seeing double, for bilingual books are everywhere, and they're steadily multiplying. For years, Tulika was the only children's publisher putting them out (as early as 1996), but now Karadi Tales and Pratham Books are also shopping for translators and dictionaries. "We actually opened Tulika with two bilingual titles, Line and Circle and Number Birds, " recounts Radhika Menon, co-founder of Tulika, and author of Line and Circle.