2 hours and 12 children NO!!!
Less time, less children, structured play or else your house will just be a free for all. (A stairgate is a good idea to stop them roaming all over the place, unless you don't mind that).
Have a clear area for jumping around and let them whack balloons about when they arrive. Then you can gather them for games.
Pass the parcel, two circles, two presents, one lot of music and a sweet in every layer with a bowl of sweets handy to give anyone who didn't get one.
Musical statues, who can keep still when the music stops (not musical chairs, its just a fight at that age).
Party bags filled and in a room near the front door so you can lift to the front door and hand out to everyone leaving (saves tripping over children as you run around the house). Have someone else cut the cake and fill the bags when you are doing games.
Tie down everything. Expect everything, including wet pants and sickness. Lots of helpers to be on toilet duty.
Gin for after