I originally bought my stroller, Peg Perego Pliko 3 Classico, for the little rubberized step in the back which, in Europe, it is promoted as a step for the second child to stand onto. In America, they do not promote it as such - I do not know why!
This is the position for two children, sanctioned by the manufacturer..
We have come up with a couple more of our own.
Firstly, when you have a car-seat in this stroller, the back seat extends over the step and the second child can no longer stand on it. Solution? The child can either sit on the rest of the back-rest facing backwards, or facing forward on their knees:
However, when you have two sleeping children and one stroller, things can get tricky. First, strap in the smallest child onto the harness that can be detached from the back of the stroller but is still fixed to the seat. Then, recline the back fully and place the larger child in the back, straddling the first.
Unfortunately, this does not bring maximum comfort to the child sitting in the front.
Try this at your child's risk! Obviously, this should only be done if you have an older and younger child - DO NOT ATTEMPT WITH TWINS, since there are restraints for only one child in a single stroller.