Browning BPS Micro. It is a 20 gauge pump. Shorter stock, 20" bbl with screw chokes. The pistol grip is shaped for a smaller hand. The stock can be replaced easily, the barrels are interchangeable with standard length barrels.
The shorter bbls put more weight between the hands, making it easier for a smaller shooter to manage. I can't tell you how many kids/women I've watched arching their backs to support the heft of a full sized gun.

http://www.browning.com/products/catalog/firearms/detail.asp?fid=011B&cid=012&tid=225

My grandson is getting one under the tree this year. His mother is looking forward to trying it.

Joe