I'm your step-mom and your dad is away on a business trip, so I want to make this day extra special and give you a birthday surprise. I greet you in your room with several balloons on the bed. I tell you that since you're a big boy now you deserve a big surprise! As your new mom I love you so much that I want to be your surprise. I'm going to use this tank of helium to turn myself into a big balloon! I play with the balloons and hold them to my belly as I tell you what I'm going to do. Remember how we bonded the other day watching your favourite childhood film, Willy Wonka and the Chocolate Factory? I noticed how hard you got when you saw Violet inflate, so I want to make you happy. I strip down and show off my step-mom bod, juicy curves in lingerie on full display for you. I strip out of my bra and panties, inserting the hose into my ass and beginning the process. I encourage you to jerk off harder and harder as my belly gets bigger and bigger and I moan. Finally when I feel I am about to pop I straddle a balloon, moaning from the pressure of my expanding stomach and the feeling of the balloon on my pussy. I love watching you jerk off son, I want your birthday cum all over my big belly