Step 1: discover that Cece's saucer is on wheels and moves. Wheel her from the kitchen where Mom is trying to make something that resembles dinner. The saucer is now perfectly placed in front of the upstairs door.
Step 2: Climb on saucer. Carefully avoid stepping on little sister so she won't cry and alert Mom to plan. Success: little sister is still cooing and smiling. Turn door knob, triggering clicking sound indicating door is now un latched. Try to open door. Oops, the saucer is blocking the entry way.
Step 3: Climb down from saucer. Door is still open. Roll saucer away from door. Sister is still smiling and Mom is still attempting to adult in the kitchen. Open door. Look at Mom. Cue shit grin.
Step 4: Eye contact made: Mom is on to the plan. Squeel with delight and run like hell up the stairs so she has to give into the chase. Repeat plan over and over and over again.