All ships we have been on the 2-5 and 6-8 groups are dropped off in the same place. the rooms are usualy connected and in some cases the room is more of a large room with dividers for the different age groups. the evenings after dinner, before the paid night owl is often a themed party. I remember things like pirate night, princess and knights, ... at those times I think some of the activities are mixed with the 2-5 and 6-8 group. they usualy came back with some sort of themed craft, and often had their faces painted.
with your kids being pretty young they will probably also checkout a phone to you. its a wireless phone that connects over the wifi so that the kids club can call you if they need to.
On embarkation day you should be able to tour the rooms and talk to the staff before the ship leaves. then I think the first time you can drop the kids off is after dinner the first night. expect a longer line that first night as everyone if figuring out the procedure and verifying the registration.
