First, make the whipped cream. In a large bowl, whip cream with a hand or stand mixer until soft peaks form. Add powdered sugar and vanilla, and beat until you have stiff peaks, being careful not to overmix.
Melt the chocolate in a double boiler or in a microwave in 30-second increments until melted. Cool slightly.
Have the kids place one piece of matzo on a large plate or platter and spread with a layer of chocolate. Top with a layer of bananas and spread with half the whipped cream. Top with another piece of matzo, a layer of chocolate, a layer of bananas, and the remaining whipped cream. Top with one more piece of matzo, a layer of chocolate, and a sprinkle of pecans.
Chill the cake in the refrigerator for at least one hour before serving. (You can make it up to 6 hours ahead.)