It is notoriously difficult to prove that a crack is the result of a manufacturing or material defect. As such, screen damage is often excluded from warranty claims.
Apple offer a limited one-year warranty - against which you might attempt to make a claim. If making a warranty claim, your should first attempt to make a claim with your retailer - as it is most often the retailer with whom your purchase contract (and therefore your warranty) principally exists. If unsuccessful, you then have the potential backup of making a claim against the manufacturer’s limited warranty.
If you had the foresight of opting to purchase Apple’s AppleCare+ plan, this being an insurance product, you will have the security of being able to make claim with Apple regardless of fault. In such circumstances, a small excess/deductible charge is made - and you will receive a replacement (usually a reconditioned iPad of the same model and specification) iPad.
Outside of warranty and AppleCare+, screen repairs through Apple are typically charged at c.60% of the cost of the iPad when it was new. In such circumstances your iPad will normally be exchanged, in lieu of an actual repair, for a reconditioned iPad.
iPad Repair – Official Apple Support