Looking for a lasting Easter gift for the kindergarten set? Spring for this, about a bunny rabbit born blue, to the amazement of its mother and siblings. The bunny seeks to frolic in the sky “ and does “ until a storm gives it second thoughts. One could view “Thunder Bunny” as an allegory for an unplanned child, at least until the end, which is a bit out of place with its metaphysical bent. But this will be lost on its target audience, who will welcome Berger’s graceful tale and bright illustrations with open arms.