I too have a 3 1/2 year old (boy), so I keep my HD guns secured. My primary HD gun is my Benelli M1S90 which I keep under the bed in a V-Line vault:
http://www.kcsafe.com/items/gun-safe...242-detail.htm
The mechanical 5 button simplex lock is quick and the vault keeps the gun secure and out of sight. An added benefit is my gun dusting is greatly reduced. I also have one of their "Top Draw" models for my HD pistol.
Chuck