My eldest son for many years has asked for Nerf guns, he has them all and the nerf n-strike maverick rev-6 is the most child friendly one around.
It is about 11inches in length and has a great comfortable handle grip and is very easy to load, all you have to do is press the black button on the left side of gun to release the six barrels and the you push the ammunition into the front of the barrels with the rubber safety heads facing forwards, then just push the barrel back into place (you are ready to play now)
To cock the gun (or set the gun up to fire) just pull back on the silver and black slide on the top of the gun until it makes a clicking noise (it is now ready to fire) Pull the trigger and the foam bullet will fire.
It will automatically click round to the next foam bullet in the barrel and you fire again, there are six barrels.
The down side to this gun and any other Nerf guns is that all round your house for many years to come you will be finding foam bullets everywhere!!
Watch out they the kids don't do head shot as the bullets come out at great speed and will injure anyone that gets one in the face.
Take care with it and have fun....we do.